Stop sending events when creating or deleting aliases

[clokep]

This implements the first task in #6898, new alias semantics:

• Update {PUT, DELETE} /_matrix/client/r0/directory/room/{roomAlias} to stop sending m.room.aliases events.
• Update DELETE /_matrix/client/r0/directory/room/{roomAlias} to check the alt_aliases in m.room.canonical_alias.

[clokep]

I believe this is ready for review. I'm not 100% thrilled about the tests (I don't think they get great coverage of the modified code) -- if anyone has advice of how to capture the result of event_creation_handler.create_and_send_nonmember_event in a unit test?

This needs corresponding changes from matrix-org/sytest#802.

[richvdh]

generally looks good, but I agree the tests are a bit weak. You should be able to check that the state of the room has been updated, possibly by calling StateHandler.get_current_state ?

There's an alternative option of testing via the REST API: have a look at something like tests/rest/client/v1/test_rooms.py for examples of some fairly complex test cases in that area. Personally, I think we're covering that base with sytest, but sometimes it's easier to go that way.

[clokep]

Added some better unit tests (which found some real bugs) and now sytests are failing! Going to look at those again.

[clokep]

I believe this is ready for another review!

[richvdh]

looks great. Nice thorough tests, thanks!