Leftover from the early opengl days.
Unused now, so delete the dead code.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-id: 20170505104101.30589-3-kraxel@redhat.com