toggle: remove the use of mx_widget_get_border_image
toggle: remove the use of mx_widget_get_border_image

The toggle is styled using a background image rather than a border image and
the border image is no longer an actor.

pwithnall/mx,jonnylamb/mx,clutter-project/mx,clutter-project/mx,jonnylamb/mx,pwithnall/mx,clutter-project/mx,jonnylamb/mx,pwithnall/mx,jonnylamb/mx,pwithnall/mx,clutter-project/mx