Deprecate RemoteViews showNext/showPrevious

Only idempotent actions should be used as RemoteViews can be reapplied
frequently. Also, these actions don't work with
partiallyUpdateAppWidget, which causes developer confusion and pain.
Developers should use setDisplayedChild instead and maintain their own
record of the current index.

Test: annotation only, validated that things still built ok
Fix: 197745933
Change-Id: I67a2615567a38dae90d693c89001adcaafba2a8e