Just mark thread chat read if the feature toggle is off
https://gitlab.com/gitlab-org/gitter/webapp/merge_requests/1622#note_236758863
The problem that is being fixed (and testing strategy at the same time):
- admin enables threaded conversations
- some threaded messages have been sent and users received unread notifications
- admin disables threaded conversations
Without this fix, there is going to be unread indicator but clicking it won't do anything.
After this fix clicking the indicator marks the chats read.
This is not optimal but it is fixing an edge case and it's only temporary till we remove the feature toggle.