Battery stats: wake locks, radio active, cleanup.

- Improve wake lock work source updates to also update the current
  history tag, in case the new work source gets recorded in the
  history.

- Fix bug in recording radio active time that was not distributing
  any time to apps.

- No longer hold a wake lock while dispatching data conn active call,
  since it comes with its own timestamp.

- Fix issue where the top app was not being cleared while the screen
  was off.

- Remove obsolete STATS_LAST stats type.

- Fix bug that was not clearing the total run time when resetting
  the stats.

Change-Id: Iabe17a9edf34f762374ae09fcffb8a819cf72e30