remove a deprecated trace of python2

Author: fchapoton

src/sage/structure/element.pxd

@@ -151,7 +151,6 @@ cdef bin_op_exception(op, x, y)
 cdef class Element(SageObject):
     cdef Parent _parent
     cpdef _richcmp_(left, right, int op)
-    cpdef int _cmp_(left, right) except -2
     cpdef base_extend(self, R)
 
     cdef getattr_from_category(self, name)

src/sage/structure/element.pyx

@@ -1159,13 +1159,6 @@ cdef class Element(SageObject):
             return True
         return NotImplemented
 
-    cpdef int _cmp_(left, right) except -2:
-        """
-        This was the old comparison framework. Now deprecated. Do not use.
-        """
-        deprecation(30130, "please use _richcmp_ for comparison methods")
-        raise NotImplementedError("__cmp__ and _cmp_ are deprecated")
-
     ##################################################
     # Arithmetic using the coercion model
     ##################################################