Fix ConcurrentModificationException in AcceptOnceConsumer

Marks AcceptOnceConsumer as ready to be removed instead
of removing from the set of callbacks while iterating

Bug: 260526969
Test: Manual, scenario where an AcceptOnceConsumer
  is created will trigger the crash provided more
  than one consumer exists
Change-Id: Ie85fd58b7d2abf0e865bca7737101ad42577e2ca