Fixes splash screen get removed directly without passing to client.

Fix regression from ag/29645700.
If an app has request to copy splash screen, and removeStartingWindow
was called before transition finish, transferSplashScreenIfNeeded will
set mRemoveAfterTransaction to AFTER_TRANSACTION_COPY_TO_CLIENT.
But then when transition finish, transferSplashScreenIfNeeded shouldn't
skip requestCopySplashScreen.

Flag: EXEMPT bugfix
Bug: 381319359
Test: run "atest SplashscreenTests" more than 10 times
Change-Id: Ia6c530b15d43e85cdbaa194054defd864e96e903