Fix issues with early-finish

There were a couple of situations where both cancel and finish
collided. In those cases make sure only one is called.

Somewhat related, launcher actually continues to use leashes
even after calling the finishCallback. Since we make leashes
for launcher anyways, just use launcher's existing leash
clean-up logic.

Bug: 235616350
Test: run/monitor wm presubmits.
      Try launching and closing apps in rapid succession.
Change-Id: I7553ba9f9bbad052632a4d8d5a7225ab6c3dbce5