User @feeds:integrations.ems.host not in room ROOM_ID when trying to remove the integration

This could be for a few reasons, but we should probably try to rejoin the room in order to remove the integration and then depart.

Also, we should bubble this error up to the UI as at the moment it just shows a generic failure message.

Trace the integration-removal flow and its UI error handling first. The change is done when removal can rejoin the room, remove the integration, and then depart, while the UI displays the underlying error instead of a generic failure message.

Written by the indexing model from the issue text.