SystemUI: Clear disappearing children and remove HeadsUp on recreate.

    - Since some views animate in and out of visibility
    the call to removeAllViews on the mStatusBarContainer may still
    keep a reference to the view.

    - Also remove mHeadsUpNotificationView from the window manager if
    it's not null.

Change-Id: I5ced26e0f36362e89779bd7c6dac4d8235e0c0e9