Removed a clear_cache statement in contrib.sites.create_default_site.

It was originally added to fix a test (refs #7514); but Site now has a
pre_save signal handler (refs #19698) to clear the cache which makes
this call redundant.

django/contrib/sites/management.py

@@ -35,5 +35,3 @@ def create_default_site(app_config, verbosity=2, interactive=True, db=DEFAULT_DB
             with connections[db].cursor() as cursor:
                 for command in sequence_sql:
                     cursor.execute(command)
-
-        Site.objects.clear_cache()