Remove now-unused django_db_models_options.py

Code that actually used it was removed in this commit:
https://github.com/edx/edx-platform/commit/26b4e30833b0410d0131c5e7bfa40b6f418ae135#diff-8d36006736e42cad141490ae17f58a89

openedx/core/djangoapps/monkey_patch/django_db_models_options.py

-"""
-Monkey patch implementation of the following _expire_cache performance improvement:
-
-https://github.com/django/django/commit/7628f87e2b1ab4b8a881f06c8973be4c368aaa3d
-
-Remove once we upgrade to a version of django which includes this fix natively!
-NOTE: This is on django's master branch but is NOT currently part of any django 1.8 or 1.9 release.
-"""
-
-from django.db.models.options import Options
-
-
-def patch():
-    """
-    Monkey-patch the Options class.
-    """
-    def _expire_cache(self, forward=True, reverse=True):
-        # pylint: disable=missing-docstring
-
-        # This method is usually called by apps.cache_clear(), when the
-        # registry is finalized, or when a new field is added.
-        if forward:
-            for cache_key in self.FORWARD_PROPERTIES:
-                if cache_key in self.__dict__:
-                    delattr(self, cache_key)
-        if reverse and not self.abstract:
-            for cache_key in self.REVERSE_PROPERTIES:
-                if cache_key in self.__dict__:
-                    delattr(self, cache_key)
-        self._get_fields_cache = {}  # pylint: disable=protected-access
-
-    # Patch constants as a set instead of a list.
-    Options.FORWARD_PROPERTIES = {'fields', 'many_to_many', 'concrete_fields',
-                                  'local_concrete_fields', '_forward_fields_map'}
-
-    Options.REVERSE_PROPERTIES = {'related_objects', 'fields_map', '_relation_tree'}
-
-    # Patch the expire_cache method to utilize constant's new set data structure.
-    Options._expire_cache = _expire_cache  # pylint: disable=protected-access