Fix up remove Wakeup preferences

Follow the bug fix addressed in http://review.cyanogenmod.org/#/c/43544/

This fix the issue both Home key wake and Volume rocker wake preferences will be displayed
if either of them activated in device config.

If both of them are not activated it looks fine because eventually Wakeup category
itself removed,though.

Change-Id: I28b7b45d209c3beb9559ed9e7b89612bf8df8bab