Resize task to fullscreen when moving from pinned stack.

- This was a regression in the original change to move the tasks to the
  fullscreen stack when the pinned stack was removed.  The task kept its
  old bounds, which causes the next animation into the PiP to not run
  since the stack bounds are taken from task bounds (which are the old
  pinned stack bounds)

Bug: 35326108
Test: run-test CtsServicesHostTestCases
Change-Id: I234910107cf62cc23b2d663161d250b9d59b3934