[KV] Remove states

To do so, had to:
* Remove PM state and put it back into the queue.
* Introduce 'active' boolean in the queue loop, which when false breaks
  out of the loop. (This is because the states collapsed into 'keep
  going' and 'finish' states.)
* Renamed extractNextAgentData() to backupPackage().
* Queue handling from backupPackage() to run().
* Agent result handling from run to backupPackage().

Bug: 110082831
Test: atest KeyValueBackupTaskTest
Test: adb shell bmgr backupnow <kv_package>
Change-Id: If6efcbf91f10426d3c955b83deb1ecd8e714f79a