Fix the toggle button flicker problem when display

- Root cause: the side effect of the parallel controller loading.
- Solution: disable the parallel approach and remove the entry point
  of parallel approach in DashboardFragment.

Fixes: 187838753
Test: Robo test for AppInfoDashboardFragment, ConfigureNotificationSettings,
      ConnectedDeviceDashboardFragment, DevelopmentSettingsDashboardFragment,
      NetworkDashboardFragment, DashboardFragment
Change-Id: If3b09c4fd6f33042e0ed38704f08e855ab8f5377

src/com/android/settings/notification/ConfigureNotificationSettings.java

@@ -96,11 +96,6 @@ public class ConfigureNotificationSettings extends DashboardFragment implements
         mNotificationAssistantPreferenceController.setBackend(new NotificationBackend());
     }
 
-    @Override
-    protected boolean isParalleledControllers() {
-        return true;
-    }
-
     private static List<AbstractPreferenceController> buildPreferenceControllers(Context context,
             Application app, Fragment host) {
         final List<AbstractPreferenceController> controllers = new ArrayList<>();