testgmenu: use the menu binding code
testgmenu: use the menu binding code

The menu tracker does a better job of this than we can, so move over to
using it instead.

This fixes issues with './testgmenu --import' not properly displaying
the language submenu.

https://bugzilla.gnome.org/show_bug.cgi?id=752016

jadahl/gtk,jigpu/gtk,Adamovskiy/gtk,grubersjoe/adwaita,jadahl/gtk,alexlarsson/gtk,chergert/gtk,Adamovskiy/gtk,grubersjoe/adwaita,davidgumberg/gtk,jigpu/gtk,jigpu/gtk,Adamovskiy/gtk,alexlarsson/gtk,chergert/gtk,jadahl/gtk,grubersjoe/adwaita,Adamovskiy/gtk,chergert/gtk,chergert/gtk,davidgumberg/gtk,Adamovskiy/gtk,grubersjoe/adwaita,alexlarsson/gtk,alexlarsson/gtk,jadahl/gtk,alexlarsson/gtk,jigpu/gtk,jigpu/gtk,chergert/gtk,jigpu/gtk,jigpu/gtk,davidgumberg/gtk,alexlarsson/gtk,grubersjoe/adwaita,jadahl/gtk,davidgumberg/gtk,chergert/gtk,alexlarsson/gtk,davidgumberg/gtk,alexlarsson/gtk,davidgumberg/gtk,Adamovskiy/gtk,davidgumberg/gtk,Adamovskiy/gtk,chergert/gtk,grubersjoe/adwaita,jigpu/gtk,jadahl/gtk,grubersjoe/adwaita,davidgumberg/gtk,chergert/gtk,grubersjoe/adwaita,jadahl/gtk,jadahl/gtk,Adamovskiy/gtk