Remove threaded-conversations room-based toggle
Part of #2471 (closed)
Makes threaded conversation always-on and removes the code that would be active when feature toggle was off.
Testing strategy
Welcome message
- Add welcome message to a room by going to the "Room Settings"
- Validate users can see it by joining the room with a different user
Threaded conversations
- Create a new room or use a room that didn't have threaded conversations enabled
- Send a threaded message
- See the thread message panel
- Refresh and open the panel again by clicking on the parent message indicator