This removes most of the code used for polylith/API mode.
This removes the `/api` internal endpoints entirely.
Binary size change roughly 5%:
```
51437560 Feb 13 10:15 dendrite-monolith-server # old
48759008 Feb 13 10:15 dendrite-monolith-server # new
```
This adds Sytest and Complement coverage reporting to the nightly
scheduled CI runs.
Fixes a few API mode related issues as well, since we seemingly never
really ran them with Complement.
Also fixes a bug related to device list changes: When we pass in an
empty `newlyLeftRooms` slice, we got a list of all currently joined
rooms with the corresponding members. When we then got the
`newlyJoinedRooms`, we wouldn't update the `changed` slice, because we
already got the user from the `newlyLeftRooms` query. This is fixed by
simply ignoring empty `newlyLeftRooms`.
This adds the possibility to run Complement with coverage enabled.
In combination with https://github.com/matrix-org/complement/pull/566 we
should then be able to extract the coverage logs, combine them with
https://github.com/wadey/gocovmerge (or similar) and upload them to
Codecov (with different flags, depending on SQLite, HTTP etc.)
