Trac #34844: removal of some unused imports about string conversion

as this may help to reduce compilation warnings

URL: https://trac.sagemath.org/34844
Reported by: chapoton
Ticket author(s): Frédéric Chapoton
Reviewer(s): Travis Scrimshaw

Author: Release Manager

src/sage/data_structures/bitset_base.pxd

@@ -37,7 +37,7 @@ from memory_allocator  cimport MemoryAllocator
 from memory_allocator.memory_allocator cimport align
 from cython.operator import preincrement as preinc
 
-from sage.cpython.string cimport char_to_str, str_to_bytes, bytes_to_str
+from sage.cpython.string cimport str_to_bytes, bytes_to_str
 from sage.libs.gmp.mpn cimport *
 from sage.libs.gmp.types cimport *
 from sage.data_structures.sparse_bitset cimport sparse_bitset_t

src/sage/interfaces/polymake.py

@@ -27,12 +27,9 @@
 
 import os
 import re
-import sys
-import time
 
 from .expect import Expect
 from .interface import (Interface, InterfaceElement, InterfaceFunctionElement)
-from sage.cpython.string import bytes_to_str, str_to_bytes
 from sage.misc.verbose import get_verbose
 from sage.misc.cachefunc import cached_method
 from sage.interfaces.tab_completion import ExtraTabCompletion

src/sage/matrix/matrix_gfpn_dense.pyx

@@ -25,19 +25,18 @@ AUTHORS:
 
 """
 
-#*****************************************************************************
+# ***************************************************************************
 #       Copyright (C) 2015 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 cysignals.memory cimport check_realloc, check_malloc, sig_free
 from cpython.bytes cimport PyBytes_AsString, PyBytes_FromStringAndSize
-from sage.cpython.string cimport str_to_bytes
 from cysignals.signals cimport sig_on, sig_off, sig_check
 cimport cython
 

src/sage/misc/parser.pyx

@@ -10,24 +10,22 @@ AUTHOR:
 
 - Robert Bradshaw 2008-04 (initial version)
 """
-
-#*****************************************************************************
+# ***************************************************************************
 #       Copyright (C) 2008 Robert Bradshaw <[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 libc.string cimport strchr
 from cpython.bytes cimport PyBytes_FromStringAndSize
 from cpython.list cimport PyList_Append
 
 import math
 
-from sage.cpython.string cimport str_to_bytes, bytes_to_str
 
 def foo(*args, **kwds):
     """