switch memcached from tcp to unix domain socket

installer/roles/local_docker/templates/credentials.py.j2

@@ -10,14 +10,4 @@ DATABASES = {
     }
 }
 
-CACHES = {
-    'default': {
-        'BACKEND': 'django.core.cache.backends.memcached.MemcachedCache',
-        'LOCATION': '{}:{}'.format("{{ memcached_hostname }}", "{{ memcached_port }}")
-    },
-    'ephemeral': {
-        'BACKEND': 'django.core.cache.backends.locmem.LocMemCache',
-    },
-}
-
 BROADCAST_WEBSOCKET_SECRET = "{{ broadcast_websocket_secret | b64encode }}"