settings: prevent multiple highlights in settings search

xe: Developer Options -> Launch Tools. The Process Stats is highlighted along
with Launch Tools, because the view of the latter is reused for the former and the
latter later gets a new view. Fix that by making sure to cancel old
highlights when triggering a new one.

Change-Id: Ibf2068628e5024d61495d4f9968811c77e120918
Signed-off-by: Jorge Ruesga <jorge@ruesga.com>