Remove redundant `event_edges.room_id` and `event_edges.is_state` columns

[richvdh]

room_id is implied by the event_id. (see also #3613)
is_state is unused since #4837.

Both are clutter and need to go away.

• ensure that nothing relies on them (Stop reading from event_edges.room_id. #12914)
• stop populating them (Clean up schema for event_edges #12893)
• delete them altogether

[MadLittleMods]

delete them altogether

At what point can we delete event_edges.is_state from our SQL queries? It seems like we have to support it forever given it's a background update to drop the rows.

I'm coming from this discussion for context: #13635 (comment)

[richvdh]

At what point can we delete event_edges.is_state from our SQL queries? It seems like we have to support it forever given it's a background update to drop the rows.

I haven't entirely figured this out yet. I think what we need to do is add a new synchronous db migration which checks if the bg update has completed, and if not, does the update synchronously. Once that has happened, it is safe to remove the conditions from the queries, and finally to drop the columns altogether.

But we shouldn't do that until it is likely that most people have completed the bg update.

[richvdh]

But we shouldn't do that until it is likely that most people have completed the bg update.

(That may well be true already. I haven't thought about this for a few months.)