Avoid remove starting window too early when playing multiple transitions

The app window would choose sync transaction for prepareSurfaceLocked
if there are more than one transacition hasn't handled in shell, so the
app window would only commit visilble after all start transactions
applied. Defer remove starting window until the transaction commit count
to zero.

Flag: EXEMPT bugfix
Bug: 362347290
Test: verify starting window won't stuck from normal launch.
Change-Id: I756e4f9930f8a91023c0e7da10f632da8839d745