Fix most unnecessary database queries in huddle creation.

This saves 2 database queries per user in the huddle when sending the
first message to a particular huddle.

(imported from commit f71aa32df846fb4b82651a93ff9608087ffcaa5a)

zephyr/lib/cache.py

@@ -88,4 +88,3 @@ def update_user_cache(sender, **kwargs):
     items_for_memcached = {}
     items_for_memcached[user_by_id_cache_key(user.id)] = (user,)
     djcache.set_many(items_for_memcached)
-