Keyboard shortcuts: minor Activity broadcast refactor

Since the broadcast intents have an action, specifying an explicit
component name is not needed. Specified only the package name and
left it for the system to resolve the full component name for the
receiver that handles the action in that package. Also got rid of
warning: "Calling a method in the system process without a
qualified user" by correctly sending the broadcast as the SYSTEM
user.

Bug: 28012198
Change-Id: Ia572fb1b7f2f3c96160d16e2842d6aff3b7f10a1