gh-40660: remove a deprecated class in structure
    
as deprecated in #26879

### 📝 Checklist

- [x] The title is concise and informative.
- [x] The description explains in detail what this PR is about.
- [x] I have linked a relevant issue or discussion.
    
URL: #40660
Reported by: Frédéric Chapoton
Reviewer(s): David Coudert

Author: Release Manager

src/sage/structure/coerce_maps.pxd

@@ -2,11 +2,7 @@
 from sage.categories.map cimport Map
 
 
-cdef class DefaultConvertMap(Map):
-    pass
-
-
-cdef class DefaultConvertMap_unique(DefaultConvertMap):
+cdef class DefaultConvertMap_unique(Map):
     pass
 
 

src/sage/structure/coerce_maps.pyx

@@ -14,19 +14,19 @@ cdef object BuiltinMethodType = type(repr)
 cdef bint print_warnings = 0
 
 
-cdef class DefaultConvertMap(Map):
+cdef class DefaultConvertMap_unique(Map):
     """
-    This morphism simply calls the codomain's element_constructor method,
-    passing in the codomain as the first argument.
-
-    EXAMPLES::
+    This morphism simply defers action to the codomain's
+    element_constructor method, WITHOUT passing in the codomain as the
+    first argument.
 
-        sage: QQ[['x']].coerce_map_from(QQ)
-        Coercion map:
-          From: Rational Field
-          To:   Power Series Ring in x over Rational Field
+    This is used for creating elements that don't take a parent as the
+    first argument to their __init__ method, for example, Integers,
+    Rationals, Algebraic Reals... all have a unique parent. It is also
+    used when the element_constructor is a bound method (whose self
+    argument is assumed to be bound to the codomain).
     """
-    def __init__(self, domain, codomain, category=None):
+    def __init__(self, domain, codomain, category=None) -> None:
         """
         TESTS:
 
@@ -49,26 +49,7 @@ cdef class DefaultConvertMap(Map):
             False
             sage: QQ[['x']].coerce_map_from(QQ)._is_coercion
             True
-
-        This class is deprecated when used directly::
-
-            sage: from sage.structure.coerce_maps import DefaultConvertMap
-            sage: DefaultConvertMap(ZZ, ZZ)
-            doctest:...: DeprecationWarning: DefaultConvertMap is deprecated, use DefaultConvertMap_unique instead.
-            This probably means that _element_constructor_ should be a method and not some other kind of callable
-            See https://github.com/sagemath/sage/issues/26879 for details.
-            Conversion map:
-              From: Integer Ring
-              To:   Integer Ring
         """
-        # The base class DefaultConvertMap is deprecated, only the
-        # derived class DefaultConvertMap_unique should be used.
-        # When removing this deprecation, this class should be merged
-        # into DefaultConvertMap_unique.
-        if not isinstance(self, DefaultConvertMap_unique):
-            from sage.misc.superseded import deprecation_cython as deprecation
-            deprecation(26879, "DefaultConvertMap is deprecated, use DefaultConvertMap_unique instead. This probably means that _element_constructor_ should be a method and not some other kind of callable")
-
         if not isinstance(domain, Parent):
             domain = Set_PythonType(domain)
         if category is None:
@@ -78,9 +59,9 @@ cdef class DefaultConvertMap(Map):
         Map.__init__(self, parent)
         self._coerce_cost = 100
         if (<Parent>codomain)._element_constructor is None:
-            raise RuntimeError("BUG in coercion model, no element constructor for {}".format(type(codomain)))
+            raise RuntimeError(f"BUG in coercion model, no element constructor for {type(codomain)}")
 
-    def _repr_type(self):
+    def _repr_type(self) -> str:
         r"""
         Return a printable type for this morphism.
 
@@ -104,7 +85,7 @@ cdef class DefaultConvertMap(Map):
         """
         cdef Parent C = self._codomain
         try:
-            return C._element_constructor(C, x)
+            return C._element_constructor(x)
         except Exception:
             if print_warnings:
                 print(type(C), C)
@@ -121,49 +102,6 @@ cdef class DefaultConvertMap(Map):
             sage: f(2/3, 4)
             2/3 + O(x^4)
         """
-        cdef Parent C = self._codomain
-        try:
-            if len(args) == 0:
-                if len(kwds) == 0:
-                    # This line is apparently never used in any tests (hivert, 2009-04-28)
-                    return C._element_constructor(C, x)
-                else:
-                    return C._element_constructor(C, x, **kwds)
-            else:
-                if len(kwds) == 0:
-                    return C._element_constructor(C, x, *args)
-                else:
-                    return C._element_constructor(C, x, *args, **kwds)
-        except Exception:
-            if print_warnings:
-                print(type(C), C)
-                print(type(C._element_constructor), C._element_constructor)
-            raise
-
-
-cdef class DefaultConvertMap_unique(DefaultConvertMap):
-    """
-    This morphism simply defers action to the codomain's
-    element_constructor method, WITHOUT passing in the codomain as the
-    first argument.
-
-    This is used for creating elements that don't take a parent as the
-    first argument to their __init__ method, for example, Integers,
-    Rationals, Algebraic Reals... all have a unique parent. It is also
-    used when the element_constructor is a bound method (whose self
-    argument is assumed to be bound to the codomain).
-    """
-    cpdef Element _call_(self, x):
-        cdef Parent C = self._codomain
-        try:
-            return C._element_constructor(x)
-        except Exception:
-            if print_warnings:
-                print(type(C), C)
-                print(type(C._element_constructor), C._element_constructor)
-            raise
-
-    cpdef Element _call_with_args(self, x, args=(), kwds={}):
         cdef Parent C = self._codomain
         try:
             if len(args) == 0:

src/sage/structure/parent.pyx

@@ -124,7 +124,7 @@ from sage.structure.category_object import CategoryObject
 from sage.structure.coerce cimport coercion_model
 from sage.structure.coerce cimport parent_is_integers
 from sage.structure.coerce_exceptions import CoercionException
-from sage.structure.coerce_maps cimport (NamedConvertMap, DefaultConvertMap,
+from sage.structure.coerce_maps cimport (NamedConvertMap,
                            DefaultConvertMap_unique, CallableConvertMap)
 from sage.structure.element cimport parent
 
@@ -1939,8 +1939,7 @@ cdef class Parent(sage.structure.category_object.CategoryObject):
 
         If a ``convert_method_name`` is provided, it creates a
         ``NamedConvertMap``, otherwise it creates a
-        ``DefaultConvertMap`` or ``DefaultConvertMap_unique``
-        depending on whether or not init_no_parent is set.
+        ``DefaultConvertMap_unique``.
 
         EXAMPLES::
 
@@ -1969,11 +1968,7 @@ cdef class Parent(sage.structure.category_object.CategoryObject):
             f = self.convert_method_map(S, m)
             if f is not None:
                 return f
-        if self._element_init_pass_parent:
-            # deprecation(26879)
-            return DefaultConvertMap(S, self, category=category)
-        else:
-            return DefaultConvertMap_unique(S, self, category=category)
+        return DefaultConvertMap_unique(S, self, category=category)
 
     def _convert_method_map(self, S, method_name=None):
         """
@@ -2274,7 +2269,6 @@ cdef class Parent(sage.structure.category_object.CategoryObject):
 
         2. If ``self._coerce_map_from_(S)`` is not exactly one of
 
-           - DefaultConvertMap
            - DefaultConvertMap_unique
            - NamedConvertMap
 
@@ -2387,7 +2381,7 @@ cdef class Parent(sage.structure.category_object.CategoryObject):
             best_mor = None
         elif user_provided_mor is True:
             best_mor = self._generic_coerce_map(S)
-            if not isinstance(best_mor, DefaultConvertMap):
+            if not isinstance(best_mor, DefaultConvertMap_unique):
                 return best_mor
             # Continue searching for better maps.  If there is something
             # better in the list, return that instead.  This is so, for