Remove redundant posting of the crossfade to the main executor

Now that the SyncTransactionQueue calls back on the main thread,
it is not necessary to move the crossfade animation to the main
thread again.

Bug: 171393374
Test: Enter PIP, resize, crossfade works
Change-Id: I4022733921f4655220a5c9ae186bf10a1838f59a
1 file changed