glx: Remove screen number from __GLXconfig

Not used.  There's no real reason to match against this instead of
matching against fbconfig or visual ID anyway.

Reviewed-by: Eric Anholt <eric@anholt.net>
Signed-off-by: Adam Jackson <ajax@redhat.com>

glx/glxscreens.h

@@ -92,8 +92,6 @@ struct __GLXconfig {
     /* OML_swap_method */
     GLint swapMethod;
 
-    GLint screen;
-
     /* EXT_texture_from_pixmap */
     GLint bindToTextureRgb;
     GLint bindToTextureRgba;