gh-35550: removing some unused imports in cython files
    
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### 📚 Description

Removing some of the (many) unused import in cython files. Found using
cython-lint

Here in libs, matrix, rings, structure folders

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### ⌛ Dependencies

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URL: #35550
Reported by: Frédéric Chapoton
Reviewer(s): Matthias Köppe

Author: Release Manager

src/sage/libs/gap/element.pyx

@@ -26,7 +26,6 @@ from .util import GAPError
 from sage.cpython.string cimport str_to_bytes, char_to_str
 from sage.misc.cachefunc import cached_method
 from sage.structure.sage_object cimport SageObject
-from sage.structure.parent import Parent
 from sage.rings.integer_ring import ZZ
 from sage.rings.rational_field import QQ
 from sage.rings.real_double import RDF

src/sage/libs/meataxe.pyx

@@ -1,15 +1,15 @@
 # distutils: libraries = mtx
 # sage_setup: distribution = sagemath-meataxe
 
-#*****************************************************************************
+# ****************************************************************************
 #       Copyright (C) 2017 Simon King <[email protected]>
 #
 # This program is free software: you can redistribute it and/or modify
 # it under the terms of the GNU General Public License as published by
 # the Free Software Foundation, either version 2 of the License, or
 # (at your option) any later version.
-#                  http://www.gnu.org/licenses/
-#*****************************************************************************
+#                  https://www.gnu.org/licenses/
+# ****************************************************************************
 
 from cpython.exc cimport PyErr_SetObject
 from cysignals.signals cimport sig_block, sig_unblock
@@ -70,7 +70,6 @@ cdef Matrix_t *rawMatrix(int Field, list entries) except NULL:
 ## to make sure that MeatAxe is initialised.
 
 from sage.cpython.string cimport str_to_bytes, char_to_str
-import os
 
 cdef void sage_meataxe_error_handler(const MtxErrorRecord_t *err):
     sig_block()

src/sage/matrix/matrix_generic_dense.pyx

@@ -13,7 +13,6 @@ from .args cimport MatrixArgs_init
 
 cimport sage.matrix.matrix as matrix
 
-from sage.structure.element cimport parent as parent_c
 
 cdef class Matrix_generic_dense(matrix_dense.Matrix_dense):
     r"""

src/sage/matrix/matrix_integer_dense.pyx

@@ -112,7 +112,7 @@ from sage.rings.integer_ring cimport IntegerRing_class
 from sage.rings.finite_rings.integer_mod_ring import IntegerModRing
 from sage.rings.polynomial.polynomial_ring_constructor import PolynomialRing
 from sage.rings.polynomial.polynomial_integer_dense_flint cimport Polynomial_integer_dense_flint
-from sage.structure.element cimport ModuleElement, RingElement, Element, Vector
+from sage.structure.element cimport Element, Vector
 from sage.structure.element import is_Vector
 from sage.structure.sequence import Sequence
 
@@ -1542,7 +1542,6 @@ cdef class Matrix_integer_dense(Matrix_dense):
         cdef Matrix_integer_dense left = <Matrix_integer_dense>self
         cdef mod_int *moduli
         cdef int i, n, k
-        cdef object parent
 
         nr = left._nrows
         nc = right._ncols

src/sage/matrix/matrix_mod2_dense.pyx

@@ -111,8 +111,7 @@ from cysignals.signals cimport sig_check, sig_on, sig_str, sig_off
 cimport sage.matrix.matrix_dense as matrix_dense
 from .args cimport SparseEntry, MatrixArgs_init
 from libc.stdio cimport *
-from sage.structure.element cimport (Matrix, Vector,
-                                     ModuleElement, Element)
+from sage.structure.element cimport (Matrix, Vector)
 from sage.modules.free_module_element cimport FreeModuleElement
 from sage.libs.gmp.random cimport *
 from sage.misc.randstate cimport randstate, current_randstate

src/sage/rings/complex_arb.pyx

@@ -186,7 +186,6 @@ from sage.rings.real_mpfi cimport RealIntervalField_class
 from sage.rings.real_mpfr cimport RealField_class, RealField, RealNumber
 from sage.rings.ring import Field
 from sage.structure.element cimport Element, ModuleElement
-from sage.structure.parent cimport Parent
 from sage.structure.unique_representation import UniqueRepresentation
 from sage.arith.long cimport is_small_python_int
 

src/sage/rings/convert/mpfi.pyx

@@ -20,7 +20,7 @@ from sage.libs.gsl.complex cimport *
 
 from sage.arith.long cimport integer_check_long
 from sage.cpython.string cimport bytes_to_str
-from sage.structure.element cimport Element, parent
+from sage.structure.element cimport Element
 
 import sage.rings.abc
 from ..integer cimport Integer

src/sage/rings/finite_rings/finite_field_base.pyx

@@ -27,15 +27,14 @@ AUTHORS:
 #  Distributed under the terms of the GNU General Public License (GPL)
 #  as published by the Free Software Foundation; either version 2 of
 #  the License, or (at your option) any later version.
-#                  http://www.gnu.org/licenses/
+#                  https://www.gnu.org/licenses/
 #*****************************************************************************
 
 cimport cython
 from cysignals.signals cimport sig_check
 from cpython.array cimport array
 
 from sage.categories.finite_fields import FiniteFields
-from sage.structure.parent cimport Parent
 from sage.misc.persist import register_unpickle_override
 from sage.misc.cachefunc import cached_method
 from sage.misc.prandom import randrange

src/sage/rings/function_field/element.pyx

@@ -67,7 +67,7 @@ AUTHORS:
 
 from sage.structure.element cimport FieldElement, RingElement, ModuleElement, Element
 from sage.misc.cachefunc import cached_method
-from sage.structure.richcmp cimport richcmp, richcmp_not_equal
+
 
 def is_FunctionFieldElement(x):
     """

src/sage/rings/function_field/element_polymod.pyx

@@ -13,7 +13,7 @@ Elements of function fields: extension
 #*****************************************************************************
 
 from sage.misc.cachefunc import cached_method
-from sage.structure.richcmp cimport richcmp, richcmp_not_equal
+from sage.structure.richcmp cimport richcmp
 from sage.structure.element cimport FieldElement, RingElement, ModuleElement, Element
 
 from sage.rings.function_field.element cimport FunctionFieldElement
@@ -76,7 +76,7 @@ cdef class FunctionFieldElement_polymod(FunctionFieldElement):
 
     def __bool__(self):
         """
-        Return True if the element is not zero.
+        Return ``True`` if the element is not zero.
 
         EXAMPLES::