Disables multidevice support in GDK.
This call must happen prior to open, gtk_init,
gtk_init_with_args or gtk_init_check in order to take effect.
Most common GTK+ applications won’t ever need to call this. Only applications that do mixed GDK/Xlib calls could want to disable multidevice support if such Xlib code deals with input devices in any way and doesn’t observe the presence of XInput 2.