Move UsageStatsManagerInternal to services.jar

UsageStatsManagerInternal is also no longer an API surface for
registration of app idle state change listeners.  AppStandbyInternal has
become a proper LocalService and interested clients can just use that
directly.

Bug: 140833849
Test: boot & run normally
Test: verify system package backup
Change-Id: Ie63f438f129cd8f41169778a3045d131ca7322fb