This patch removes the `visible_rooms` sliding sync list from
`RoomListService`. As we are taking the path of doing client-side
sorting, the ordering of the server-side will most likely always
mismatch the ordering of the client-side, thus using `visible_rooms`
with room indices make no sense (indices from server-side won't map
indices on the client-side, so room ranges from client-side won't map
what the server knows).
We used to use `visible_rooms` to “preload” the timeline of rooms in
the user app viewport, with a `timeline_limit` of 20. This should be
replaced by room subscriptions starting from now. For the moment, the
user of `RoomListService` is responsible to do that manually. Maybe
`RoomListService` will handle that automatically in the future.
Ivan Enderlin
7aa7d1ca53