Once again, cancel all when notifications canceled for pkg.

Right now this only works if you go through the front door
(using setNotificationsEnabledForPackage()); if you set the
AppOps for a package otherwise the existing notifications
will not be cleared (but new ones will be blocked). Since
there's no UI for modifying AppOps today this shouldn't be a
problem.

Bug: 8489214
Change-Id: I84f8c76a0d03959127e9076ab2b7d37dbdaebb17