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/OneHandedEnablePreferenceController.java

@@ -32,8 +32,7 @@ public class OneHandedEnablePreferenceController extends SettingsMainSwitchPrefe
 
     @Override
     public int getAvailabilityStatus() {
-        return OneHandedSettingsUtils.isFeatureAvailable(mContext)
-                ? AVAILABLE : UNSUPPORTED_ON_DEVICE;
+        return AVAILABLE;
     }
 
     @Override