testgtk: Remove handlebox example
testgtk: Remove handlebox example

Rather than keeping it and enabling deprecated code in testgtk I decided
to delete the example. The warnings from testgtk about deprecated code
are too useful IMO.
Should we need it again, we can make it into its own test, or add a
testgtkdeprecated.

grubersjoe/adwaita,jessevdk/gtk,Sidnioulz/SandboxGtk,jadahl/gtk,msteinert/gtk,Lyude/gtk-,Adamovskiy/gtk,jigpu/gtk,davidgumberg/gtk,ebassi/gtk,jessevdk/gtk,jigpu/gtk,jessevdk/gtk,chergert/gtk,ebassi/gtk,alexlarsson/gtk,davidt/gtk,Distrotech/gtk2,alexlarsson/gtk,bratsche/gtk-,ebassi/gtk,Adamovskiy/gtk,Sidnioulz/SandboxGtk,davidt/gtk,chergert/gtk,grubersjoe/adwaita,alexlarsson/gtk,davidgumberg/gtk,jessevdk/gtk,ahodesuka/gtk,jadahl/gtk,msteinert/gtk,Lyude/gtk-,msteinert/gtk,chergert/gtk,davidt/gtk,Lyude/gtk-,Distrotech/gtk2,bratsche/gtk-,alexlarsson/gtk,ahodesuka/gtk,bratsche/gtk-,Adamovskiy/gtk,Sidnioulz/SandboxGtk,davidt/gtk,ebassi/gtk,jigpu/gtk,chergert/gtk,bratsche/gtk-,Adamovskiy/gtk,chergert/gtk,davidt/gtk,davidgumberg/gtk,Adamovskiy/gtk,grubersjoe/adwaita,msteinert/gtk,grubersjoe/adwaita,jadahl/gtk,jessevdk/gtk,jigpu/gtk,grubersjoe/adwaita,davidgumberg/gtk,jadahl/gtk,ahodesuka/gtk,ahodesuka/gtk,jadahl/gtk,ebassi/gtk,grubersjoe/adwaita,Lyude/gtk-,jigpu/gtk,jigpu/gtk,Adamovskiy/gtk,jessevdk/gtk,Distrotech/gtk2,ahodesuka/gtk,Lyude/gtk-,grubersjoe/adwaita,chergert/gtk,davidt/gtk,ebassi/gtk,chergert/gtk,Distrotech/gtk2,msteinert/gtk,jadahl/gtk,davidgumberg/gtk,Lyude/gtk-,chergert/gtk,jadahl/gtk,davidgumberg/gtk,Distrotech/gtk2,Adamovskiy/gtk,Distrotech/gtk2,alexlarsson/gtk,jigpu/gtk,bratsche/gtk-,Sidnioulz/SandboxGtk,Lyude/gtk-,alexlarsson/gtk,jigpu/gtk,alexlarsson/gtk,davidgumberg/gtk,Sidnioulz/SandboxGtk,davidgumberg/gtk,jessevdk/gtk,msteinert/gtk,jadahl/gtk,Sidnioulz/SandboxGtk,Lyude/gtk-,ahodesuka/gtk,ahodesuka/gtk,ahodesuka/gtk,bratsche/gtk-,alexlarsson/gtk,grubersjoe/adwaita,Adamovskiy/gtk