gh-35765: more fixes for superfluous cython imports
    
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### 📚 Description

found by cython-lint ; removing a few more useless cython imports

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URL: #35765
Reported by: Frédéric Chapoton
Reviewer(s): Matthias Köppe

Author: Release Manager

src/sage/algebras/octonion_algebra.pyx

@@ -5,16 +5,15 @@ AUTHORS:
 
 - Travis Scrimshaw (2023-05-06): Initial version
 """
-
-#*****************************************************************************
+# ****************************************************************************
 #       Copyright (C) 2023 Travis Scrimshaw <tcscrims at gmail.com>
 #
 # 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 sage.misc.cachefunc import cached_method
 from sage.misc.functional import sqrt
@@ -27,7 +26,7 @@ from sage.modules.free_module import FreeModule
 from sage.categories.magmatic_algebras import MagmaticAlgebras
 from sage.categories.rings import Rings
 from sage.categories.metric_spaces import MetricSpaces
-from sage.categories.fields import Fields
+
 
 cdef class Octonion_generic(AlgebraElement):
     r"""

src/sage/graphs/hyperbolicity.pyx

@@ -146,7 +146,7 @@ Methods
 # 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 libc.string cimport memset
@@ -157,7 +157,6 @@ from memory_allocator cimport MemoryAllocator
 from sage.graphs.distances_all_pairs cimport c_distances_all_pairs
 from sage.arith.misc import binomial
 from sage.rings.integer_ring import ZZ
-from sage.data_structures.bitset import Bitset
 from sage.graphs.base.static_sparse_graph cimport short_digraph
 from sage.graphs.base.static_sparse_graph cimport init_short_digraph
 from sage.graphs.base.static_sparse_graph cimport free_short_digraph

src/sage/graphs/strongly_regular_db.pyx

@@ -3159,7 +3159,6 @@ def _build_small_srg_database():
     from sage.graphs.generators.smallgraphs import M22Graph
     from sage.graphs.generators.smallgraphs import SimsGewirtzGraph
     from sage.graphs.generators.smallgraphs import HoffmanSingletonGraph
-    from sage.graphs.generators.smallgraphs import SchlaefliGraph
     from sage.graphs.generators.smallgraphs import HigmanSimsGraph
     from sage.graphs.generators.smallgraphs import IoninKharaghani765Graph
     from sage.graphs.generators.smallgraphs import JankoKharaghaniGraph

src/sage/libs/mpmath/ext_libmp.pyx

@@ -1,10 +1,8 @@
 """
 Faster versions of some key functions in mpmath.libmp
 """
-
 from .ext_impl cimport *
 from sage.libs.gmp.all cimport *
-from sage.rings.integer cimport Integer
 
 from .ext_impl import exp_fixed, cos_sin_fixed, log_int_fixed
 

src/sage/matrix/matrix_symbolic_sparse.pyx

@@ -163,15 +163,14 @@ Check that :issue:`35653` is fixed::
     [  0 1/x]
 """
 from sage.rings.polynomial.polynomial_ring_constructor import PolynomialRing
-from sage.structure.element cimport ModuleElement, RingElement, Element
 from sage.structure.factorization import Factorization
 
 from .matrix_generic_sparse cimport Matrix_generic_sparse
 from .constructor import matrix
 
 cdef maxima
 
-from sage.calculus.calculus import symbolic_expression_from_maxima_string, maxima
+from sage.calculus.calculus import maxima
 
 cdef class Matrix_symbolic_sparse(Matrix_generic_sparse):
     def echelonize(self, **kwds):

src/sage/modular/pollack_stevens/dist.pyx

@@ -18,14 +18,14 @@ REFERENCES:
 - [PS2011]_
 """
 
-#*****************************************************************************
+# ****************************************************************************
 #       Copyright (C) 2012 Robert Pollack <[email protected]>
 #
 #  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/
+# ****************************************************************************
 
 from sage.structure.richcmp cimport richcmp_not_equal, rich_to_bool
 from sage.rings.integer_ring import ZZ
@@ -38,20 +38,10 @@ from sage.matrix.constructor import matrix
 from sage.structure.element cimport Element
 import operator
 from sage.rings.padics.padic_generic import pAdicGeneric
-from sage.rings.padics.padic_capped_absolute_element cimport pAdicCappedAbsoluteElement
-from sage.rings.padics.padic_capped_relative_element cimport pAdicCappedRelativeElement
-from sage.rings.padics.padic_fixed_mod_element cimport pAdicFixedModElement
 from sage.rings.integer cimport Integer
 from sage.misc.verbose import verbose
 from sage.rings.infinity import Infinity
 
-from sage.libs.flint.nmod_poly cimport (nmod_poly_init2_preinv,
-                                        nmod_poly_set_coeff_ui,
-                                        nmod_poly_inv_series,
-                                        nmod_poly_mullow,
-                                        nmod_poly_pow_trunc,
-                                        nmod_poly_get_coeff_ui, nmod_poly_t)
-
 #from sage.libs.flint.ulong_extras cimport *
 
 from .sigma0 import Sigma0

src/sage/numerical/backends/ppl_backend.pyx

@@ -9,23 +9,24 @@ AUTHORS:
   constraints and objective function (:trac:`16755`)
 """
 
-#*****************************************************************************
+# ****************************************************************************
 #       Copyright (C) 2010 Risan <[email protected]>
 #       Copyright (C) 2014 Jeroen Demeyer <[email protected]>
 #
 #  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/
+# ****************************************************************************
 
 from sage.numerical.mip import MIPSolverException
-from ppl import MIP_Problem, Variable, Variables_Set, Linear_Expression, Constraint, Generator
+from ppl import MIP_Problem, Variable, Variables_Set, Linear_Expression
 from sage.rings.integer cimport Integer
 from sage.rings.rational cimport Rational
 from .generic_backend cimport GenericBackend
 from copy import copy
 
+
 cdef class PPLBackend(GenericBackend):
 
     """

src/sage/schemes/elliptic_curves/descent_two_isogeny.pyx

@@ -13,7 +13,7 @@ Descent on elliptic curves over `\QQ` with a 2-isogeny
 # ***************************************************************************
 
 from cysignals.memory cimport sig_malloc, sig_free
-from cysignals.signals cimport sig_on, sig_off
+from cysignals.signals cimport sig_on
 
 from sage.rings.integer_ring import ZZ
 from sage.rings.polynomial.polynomial_ring import polygen