Clean up previous DA organizer when registering

- There is no guarantee that binderDied() will come in for the old
  process before it tries to re-register. Instead, force clean up
  the existing organizer if another organizer is registered for the
  same feature
- Also unlink the death recipient when unregistering/cleaning up the
  organizer

Bug: 190786551
Test: Kill SysUI and ensure it doesn't throw
Change-Id: I1334076cd385955fac7f518356a9703d1544c9bd