Fix issue with PiP callbacks not being handled for secondary users.

- With ag/1767862, we do not persist PiP across users, so there is no
  need for additional logic in SystemUI to dedupe these calls. Since
  PiP is managed in the primary user's SystemUI process, this logic
  was prevening the relaunching of the activity.

Bug: 64316002
Test: Launch PiP from a secondary user, restart the activity and
      ensure that it is brought to fullscreen.

Change-Id: I49db5cab9f0be7366390d1e36edcaf4d6b05717a