Uniformize spam-checker API, part 4: port other spam-checker callbacks to return `Union[Allow, Codes]`. (#12857)

Co-authored-by: Brendan Abolivier <babolivier@matrix.org>

Removes the `register_noop_background_update` and deletes the background
updates directly in a delta file.

It's now implied by the room_version property on the event.

Instead, use the `room_version` property of the event we're checking.

The `room_version` was originally added as a parameter somewhere around #4482,
but really it's been redundant since #6875 added a `room_version` field to `EventBase`.

Instead, use the `room_version` property of the event we're validating.

The `room_version` was originally added as a parameter somewhere around #4482,
but really it's been redundant since #6875 added a `room_version` field to `EventBase`.

In practice, when we run the auth rules, all of the events have the right room
version. Let's stop building Room V1 events for these tests and use the right
version.

This reverts commit ae09cc2e.

This commit was intended for a different branch.

Missed by #12475.

* Clarifies comments and documentation.
* Adds type-hints.
* Fixes Python 3 compatibility (and runs pyupgrade).
* Updates for changes in Synapse internals.

The `room_id` field was removed from MSC2946 before
it was accepted. It was initially kept for backwards compatibility
and should be removed now that the stable form of the API
is used.

This change only stops Synapse from validating that it is returned,
a future PR will remove returning it as part of the response.

... to help us keep track of these things

MSC3715 defines this parameter, but the unstable version of it should be
behind an experimental flag.

Co-authored-by: Brendan Abolivier <babolivier@matrix.org>

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>

* Reword failure message about `await_result=False`
* Use `reactor.advance()` instead of `reactor.pump()`
* Raise `AssertionError`s ourselves
* Un-instance method `_test_disconnect`
* Replace `ThreadedMemoryReactorClock` with `MemoryReactorClock`

* Add tests for `/rooms/<room_id>/members` cancellation.
* Add tests for `/rooms/<room_id>/state` cancellation.

Signed-off-by: Sean Quah <seanq@element.io>

Return the same error message from `/login` when password is incorrect and when account doesn't exist. (#12738)

* Don't pull out state for catchup

* Newsfile

* Merge newsfile

By always using delete_devices and sometimes passing a list
with a single device ID.

Previously these methods had gotten out of sync with each
other and it seems there's little benefit to the single-device
variant.

* Remove an unused stream ID generator.
* Remove the now unused remote profile cache.

Reducing the amount of state we pull from the DB is useful as fetching state is expensive in terms of DB, CPU and memory.