Remove first icon from notification footer after it animates.

Before, we had a hack where the notifation view would tell the
footer to trim its notifications, which is inefficient and ugly
since we already know exactly what notification to remove. So
now we move the relevant removal logic (keeping things like the
overflow text in sync) to a removeViewFromIconRow() that is
used after the icon animates as well as when trimming notifications.

Bug: 32410600
Change-Id: I19e54e0c28daea869b45649c7f5c74843412bb86