Clean up interaction with confirmation dialog

It now only sends a single 'done' event, which we can use .once on

Relies on I4f485d4f in OOjs UI.

New changes:
418cd67 Update OOjs UI to v0.1.0-pre (0f101c6f5d)

Bug: 65571
Change-Id: I19aa65612bf02bed056de292f212d2f5732a8fec