Revert incorrect changes to where we send events

synapse/handlers/_base.py

@@ -133,6 +133,7 @@ class BaseHandler(object):
         for k, s in context.current_state.items():
             try:
                 if k[0] == EventTypes.Member:
+                    if s.content["membership"] == Membership.JOIN:
                         destinations.add(
                             UserID.from_string(s.state_key).domain
                         )