Remove ability for AS users to call /events and /sync

This functionality has been deprecated for a while as well as being
broken for a while. Instead of fixing it lets just remove it entirely.

See: https://github.com/matrix-org/matrix-doc/issues/1144

synapse/handlers/room.py

@@ -475,12 +475,9 @@ class RoomEventSource(object):
             user.to_string()
         )
         if app_service:
-            events, end_key = yield self.store.get_appservice_room_stream(
-                service=app_service,
-                from_key=from_key,
-                to_key=to_key,
-                limit=limit,
-            )
+            # We no longer support AS users using /sync directly.
+            # See https://github.com/matrix-org/matrix-doc/issues/1144
+            raise NotImplementedError()
         else:
             room_events = yield self.store.get_membership_changes_for_user(
                 user.to_string(), from_key, to_key