Remove the old battery page

This CL removes PowerUsageSummaryLegacy and PowerUsageAdvancedLegacy
and their related layouts and strigns.

Also remove the isBatteryV2Enabled method in feature provider.

Change-Id: I1ec30f713d733ed24335a3e698fb515751232948
Fixes: 76027338
Test: robo test still pass

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

@@ -105,11 +105,6 @@ public interface PowerUsageFeatureProvider {
      */
     String getAdvancedUsageScreenInfoString();
 
-    /**
-     * Checks whether to display the battery v2.
-     */
-    boolean isBatteryV2Enabled();
-
     /**
      * Returns a signal to indicate if the device will need to warn the user they may not make it
      * to their next charging time.