Fix a flicker when window is removed during entering animation

When animation is started with saved surfaces, app may decide to
remove one of the child windows during early animation and replace
it with a new window. This causes the app below (usually Recents)
to show through for one or more frames.

If we started animation early with a window, delay removal of
that window until the app is allDrawn in the "traditional sense"
(i.e. allDrawn without using any saved surfaces).

bug: 28742353
Change-Id: I4ef663a947b737aae96c3ccfe13a9f4c1d0567f0