Reset the remote transition references on the main shell thread

- Hypothetically, if the remote transition references is cleared on the
  binder thread, a pending to-be-merged transition would preempt the
  onTransitionFinished() callback leading to a crash
- Also add additional logs that can confirm this case if it happens
  again (ie. log that the remote transition is calling finish in
  addition to the basic transition finished/merged logs)

Bug: 285935417
Test: Presubmit
Change-Id: Ie0efc15b928010fab3e88f358e3d474e38c138f0