Defer remove splash screen window if it is inTransition.

When another transition happen after first open app transition, e.g.
create task fragment, the surface of app window may shown after
transition start. If we remove starting window right after app report
drawn, there might show a blank while transition is playing.

Bug: 276692049
Test: manual launch app from notification shade several times, verify
no blank window occur.

Change-Id: If606fe2cab78143b1a80c1819088d67b6396a953