Fix AlwaysOnTop stack may covered by RemoteAnimation

Now with hierarachical animation, the layer of
RecentsAnimation / RemoteAnimation are controlled by system.

Now Launcher side don't need to have other way to set layer for ZBoost
case, so remove setLayer & withLayer related logics for cleaning up.

Fix: 151024899
Test: manual, launch google map app -> enter PiP mode,
      swipe up to overview screen or launch activity from shortcut,
      make sure the PiP window is not covered by other apps.

Change-Id: I8028cd50d66f7d77e5d1ec6514e953c8be9935d6