gtk: disable mnemonics in gtkrc.key.mac, they don't exist on the Mac
gtk: disable mnemonics in gtkrc.key.mac, they don't exist on the Mac

Distrotech/gtk,Unity-Technologies/gtk,johne53/MB3Gtk-2,Unity-Technologies/gtk,Unity-Technologies/gtk,Distrotech/gtk,johne53/MB3Gtk-2,johne53/MB3Gtk-2,johne53/MB3Gtk-2,Distrotech/gtk,Unity-Technologies/gtk,Distrotech/gtk,johne53/MB3Gtk-2,Unity-Technologies/gtk,Distrotech/gtk