Making "Battery Saver" use MasterSwitchPreference.

By using MasterSwitchPreference, we make "battery saver" to have
two parts: left part is the clickable summary jumping to other
fragment while right part is a switch toggle.

Also remove the previous battery saver preference.

Bug: 34279051
Test: RunSettingsRoboTests

Change-Id: If36fa9741e413a9bbdd57fa67a2c15b6e457afd7

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

@@ -158,6 +158,7 @@ public class PowerUsageSummary extends PowerUsageBase {
         final List<PreferenceController> controllers = new ArrayList<>();
         controllers.add(new AutoBrightnessPreferenceController(context));
         controllers.add(new TimeoutPreferenceController(context));
+        controllers.add(new BatterySaverController(context, getLifecycle()));
         return controllers;
     }