Remove redundant swipe down notification and one handed sub settings

1. Remove "Swipe down for notification" item code.
2. Remove "Exit when switching apps & "Timeout" items code.

Bug: 175851783

Test: build & verify Settings > System > Gestures
Test: make RunSettingsRoboTests ROBOTEST_FILTER=
      "com.android.settings.gestures
      .OneHandedEnablePreferenceControllerTest"

Change-Id: I77be5ff5542f6310fa0b9649ddfc1d3c16fa4261

src/com/android/settings/gestures/OneHandedSettingsUtils.java

@@ -189,15 +189,6 @@ public class OneHandedSettingsUtils {
                 Settings.Secure.NAVIGATION_MODE, 2 /* fully gestural */, sCurrentUserId);
     }
 
-    /**
-     *
-     * @param context App context
-     * @return Support One-Handed mode feature or not.
-     */
-    public static boolean isFeatureAvailable(Context context) {
-        return isSupportOneHandedMode() && getNavigationBarMode(context) != 0;
-    }
-
     /**
      * Registers callback for observing Settings.Secure.ONE_HANDED_MODE_ENABLED state.
      * @param callback for state changes