Don't send redundant WCT for exit-pip finishTransition

exit-pip reaches the end state at the beginning of the transition,
sending another WCT at finish can erroneously interleave with
other transitions (esp. other pip transitions) causing the system
to end up in a bad state because it can effectively re-apply
the expand-pip WCT after a transition it was originally ahead of.
It is also redundant.

Bug: 231150615
Test: atest PinnedStackTests#testPipUnPipOverHome
Change-Id: Ica657d7d610226a09f34375685ed4089a63d4e92