Ignore invisible activity change from finishing transition

There could be 2 cases that the change of "returning to app"
from recents (home) transition is visible in next transition.

1. Open a translucent activity in the same task.
 Transition type=OPEN {
  TaskX-activityA m=OPEN f=TRANSLUCENT
  TaskHome m=TO_BACK f=SHOW_WALLPAPER
 }

2. Finish an activity and the next activity is in the same task.
 Transition type=CLOSE {
  TaskX-activityB m=CLOSE
  TaskX-activityA m=TO_FRONT
  TaskX m=CHANGE f=MOVE_TO_TOP
  TaskHome m=TO_BACK f=SHOW_WALLPAPER
 }

Because the occluded change should be invisible, simply remove it
to avoid putting it on transition root or disturbing the selection
of animation style.

Bug: 306181322
Bug: 314252039
Test: Launch 2 activities in the same task. The first one will
      sleep 300ms in onResume (easier to tap nav bar).
      Finish the second one and tap nav bar quickly.
      Home should not flash a few frames.

Change-Id: I6e8e6a2afed88268babee4d3c68c79d3b97023e5