Remove starting window via legacy method before the display is ready.

If the display isn't ready, Core won't send the transition ready and
the rest of the events to Shell. Therefore, the starting window should
be removed via legacy method, without depending on Shell.

Flag: com.android.window.flags.remove_starting_in_transition
Bug: 418904148
Test: Launch an app during mActivityManager.bootAnimationComplete(),
verify the splash screen will be removed without transition.
Change-Id: Ibe407195c69797e0f6e2c7e6fda766fae5bc58a2