Update ActivityTransitionAnimatorTest to work with the new transaction.

Ordinarily we would be able to use a stubbed transaction to avoid the
`reparent` operation which doesn't work in tests. However, because we
are still using the remote animation wrapper around RemoteTransition,
we can't directly inject such transaction. For now we just disable
the `reparent` operation in tests.

Bug: 390422470
Flag: EXEMPT test only
Test: atest ActivityTransitionAnimatorTest
Change-Id: I733b3768ea7d1ecec85896c3d66ef9a9561f2bb9