Remove aliases from /publicRooms response (#3624)

Through attempting to land [Synapse#11667](https://github.com/matrix-org/synapse/pull/11667) it was found that Synapse doesn't return the `aliases` property on `/publicRooms` as it was [removed](https://github.com/matrix-org/synapse/pull/6970) by a [tracking issue](https://github.com/matrix-org/synapse/issues/6898) referencing [MSC2432](https://github.com/matrix-org/matrix-doc/pull/2432) as its base. Though MSC2432 does not make mention of this, the [document](https://docs.google.com/document/d/1NNDkobiFLeUkJtyj0H6qvKIedgvIkZnFKo78-03cGEk/edit) the MSC is based upon makes deliberate effort to mention the endpoint and the removal of `aliases`. Thus, it is determined as a likely accidental omission from the formal MSC and therefore the formal spec.

This has been corrected here by amending the MSC (per the process) and removing the field, basing itself off of the [spec PR for spaces](https://github.com/matrix-org/matrix-doc/pull/3610) for diff clarity.

data/api/client-server/space_hierarchy.yaml

@@ -100,7 +100,6 @@ paths:
                   "join_rule": "public",
                   "room_type": "m.space",
                   "num_joined_members": 42,
-                  "aliases": ["#general:example.org"],
                   "canonical_alias": "#general:example.org",
                   "children_state": [
                     {