Revert "filter out m.room.aliases from the CS API until a better solu…

…tion is specced (matrix-org#6878)"

This reverts commit 8e64c5a.

synapse/visibility.py

@@ -122,13 +122,6 @@ def allowed(event):
         if not event.is_state() and event.sender in ignore_list:
             return None
 
-        # Until MSC2261 has landed we can't redact malicious alias events, so for
-        # now we temporarily filter out m.room.aliases entirely to mitigate
-        # abuse, while we spec a better solution to advertising aliases
-        # on rooms.
-        if event.type == EventTypes.Aliases:
-            return None
-
         # Don't try to apply the room's retention policy if the event is a state event, as
         # MSC1763 states that retention is only considered for non-state events.
         if apply_retention_policies and not event.is_state():