gallium/x11: remove empty GLX_SGIX_swap_barrier stubs

The extension was never implemented. Quick search suggests:
 - no actual users (on my Arch setup)
 - the Nvidia driver does not implement the extension

Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
Acked-by: Ian Romanick <ian.d.romanick@intel.com>
Acked-by: Brian Paul <brianp@vmware.com>
Reviewed-by: Adam Jackson <ajax@redhat.com>

src/gallium/state_trackers/glx/xlib/glx_api.c

@@ -2659,27 +2659,6 @@ glXJoinSwapGroupSGIX(Display *dpy, GLXDrawable drawable, GLXDrawable member)
 
 
 
-/*** GLX_SGIX_swap_barrier ***/
-
-PUBLIC void
-glXBindSwapBarrierSGIX(Display *dpy, GLXDrawable drawable, int barrier)
-{
-   (void) dpy;
-   (void) drawable;
-   (void) barrier;
-}
-
-PUBLIC Bool
-glXQueryMaxSwapBarriersSGIX(Display *dpy, int screen, int *max)
-{
-   (void) dpy;
-   (void) screen;
-   (void) max;
-   return False;
-}
-
-
-
 /*** GLX_SUN_get_transparent_index ***/
 
 PUBLIC Status

src/gallium/state_trackers/glx/xlib/glx_getproc.c

@@ -150,10 +150,6 @@ static struct name_address_pair GLX_functions[] = {
    /*** GLX_SGIX_swap_group ***/
    { "glXJoinSwapGroupSGIX", (__GLXextFuncPtr) glXJoinSwapGroupSGIX },
 
-   /*** GLX_SGIX_swap_barrier ***/
-   { "glXBindSwapBarrierSGIX", (__GLXextFuncPtr) glXBindSwapBarrierSGIX },
-   { "glXQueryMaxSwapBarriersSGIX", (__GLXextFuncPtr) glXQueryMaxSwapBarriersSGIX },
-
    /*** GLX_SUN_get_transparent_index ***/
    { "glXGetTransparentIndexSUN", (__GLXextFuncPtr) glXGetTransparentIndexSUN },