Remove EXTRA_DELETE_AFTER_USE and update descriptions accordingly.

As per UX, we're removing the EXTRA_DELETE_AFTER_USE flag. Instead,
apps that pick up these intents should automatically delete alarms
and timers, unless the user is taken into the app to explicicitly
specify the time/length.

Change-Id: Ibd582788c04e121427467f6549759c8b7706df8c