Do not bundle aggregations for APIs which shouldn't include them. (#11592)

And make bundling aggregations opt-in, instead of opt-out to avoid
having APIs to include extraneous data (and being much heavier than
necessary).

synapse/handlers/events.py

@@ -123,8 +123,6 @@ class EventStreamHandler:
                 events,
                 time_now,
                 as_client_event=as_client_event,
-                # Don't bundle aggregations as this is a deprecated API.
-                bundle_aggregations=False,
             )
 
             chunk = {