TV PIP: Dismiss notification when the PIP is over

This fixes the regression caused by the previous commit
bad26692 Set notification TAG and style in TV PIP notification

Bug: 37249867
Test: Manual test (PIP notification UI was dismissed after closing th
    PIP by notification UI, or PIP controller dialog. Also checked that
    the notification UI was dismissed after the the PIPed activity
    becomes fullscreen.)
Change-Id: I4dc6d1ee8035f89583a5fb49aa6c8fdc40bb49a0