Remove the tasks created by the organizer when it dies.

- Instead of moving these tasks to a different organizer they are now removed.
- This is done because it makes sense for the tasks to end along with the
  organizer that created them.

Bug: b/223420767
Test: atest WindowOrganizerTests
Change-Id: Ibb53ce28d865e83bbcefc35f5625b3a71b6ee766