Remove CounterRotator surface in finishTransaction

Before, the surface will be removed, and the children will be reparented
to root in a separate transaction when animation is done. That would
cause a flicker because the reparented children may be above the
rotation activity.

Bug: 206094140
Test: manually test expanding PIP
Change-Id: I0f16b7590d4bd0f4c377158d555cb94f28f134cd