Remove DatabaseFeatures.is_mongodb_6_3

Follow up to ce390e8.

Author: timgraham

django_mongodb_backend/features.py

@@ -597,10 +597,6 @@ def django_test_skips(self):
         skips.update(self._django_test_skips)
         return skips
 
-    @cached_property
-    def is_mongodb_6_3(self):
-        return self.connection.get_database_version() >= (6, 3)
-
     @cached_property
     def supports_atlas_search(self):
         """Does the server support Atlas search queries and search indexes?"""