gtkplug.c: remove draw function, not needed
gtkplug.c: remove draw function, not needed

Background will be rendered by parent class - GtkWindow.

https://bugzilla.gnome.org/show_bug.cgi?id=754854

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