Use presence replication stream to invalidate cache

Instead of using the cache invalidation replication stream to invalidate
the _get_presence_cache, we can instead rely on the presence replication
stream. This reduces the amount of replication traffic considerably.

synapse/replication/slave/storage/presence.py

@@ -57,5 +57,6 @@ class SlavedPresenceStore(BaseSlavedStore):
                 self.presence_stream_cache.entity_has_changed(
                     user_id, position
                 )
+                self._get_presence_for_user.invalidate((user_id,))
 
         return super(SlavedPresenceStore, self).process_replication(result)

synapse/storage/presence.py

@@ -85,8 +85,8 @@ class PresenceStore(SQLBaseStore):
                 self.presence_stream_cache.entity_has_changed,
                 state.user_id, stream_id,
             )
-            self._invalidate_cache_and_stream(
-                txn, self._get_presence_for_user, (state.user_id,)
+            txn.call_after(
+                self._get_presence_for_user, (state.user_id,)
             )
 
         # Actually insert new rows