Fix surface release race when using Shell Transitions

Shell Transitions operates on the leashes both before and
after the animation in order to adapt shell transit to the
legacy transit impls in launcher.

This means we can't release the surfaces before the finish
callback. Since the finish callback provides a convenient place
to release the surfaces anyways, we can effectively disable
the release here.

Bug: 186158221
Test: enable shell transit, physically rotate to landscape,
      launch messages and then close it (back-gesture) repeatedly
      and observe that launcher doesn't crash.
Change-Id: Ibdc958b1fd18d66a013d94b70772ce49409fb4c1