Never store battery stats for cache

In PowerUsageBase, it will store battery stats if it has a configuration
change, which will make BatteryStatsLoaderHelper never get the correct
battery stats because it uses Bundle.EMPTY as the bundle message.

This cl:
1. Remove the store action even though it is configuration change.
2. Always use null to get battery stats
3. Always start a battery status check in register()

Bug: 63658232
Test: RunSettingsRoboTests
Change-Id: Ifbf970c63378ed66dddcdae4d952b7d1fd84216a

src/com/android/settings/fuelgauge/BatteryUtils.java

@@ -370,6 +370,7 @@ public class BatteryUtils {
     public void initBatteryStatsHelper(BatteryStatsHelper statsHelper, Bundle bundle,
             UserManager userManager) {
         statsHelper.create(bundle);
+        statsHelper.clearStats();
         statsHelper.refreshStats(BatteryStats.STATS_SINCE_CHARGED, userManager.getUserProfiles());
     }