include: Revert out the update of the Khronos GLX extension header.

They made a mistake in the MESA_swap_control XML, which I'm pursuing in
their github.  Until then, we can just back this piece out.

Tested-by: Mark Janes <mark.a.janes@intel.com>
Reviewed-by: Mark Janes <mark.a.janes@intel.com>

include/GL/glxext.h

@@ -34,7 +34,7 @@ extern "C" {
 **   https://github.com/KhronosGroup/OpenGL-Registry
 */
 
-#define GLX_GLXEXT_VERSION 20170926
+#define GLX_GLXEXT_VERSION 20170728
 
 /* Generated C header for:
  * API: glx
@@ -503,16 +503,6 @@ Bool glXSet3DfxModeMESA (int mode);
 #endif
 #endif /* GLX_MESA_set_3dfx_mode */
 
-#ifndef GLX_MESA_swap_control
-#define GLX_MESA_swap_control 1
-typedef int ( *PFNGLXGETSWAPINTERVALMESAPROC) (void);
-typedef void ( *PFNGLXSWAPINTERVALMESAPROC) (unsigned int interval);
-#ifdef GLX_GLXEXT_PROTOTYPES
-int glXGetSwapIntervalMESA (void);
-void glXSwapIntervalMESA (unsigned int interval);
-#endif
-#endif /* GLX_MESA_swap_control */
-
 #ifndef GLX_NV_copy_buffer
 #define GLX_NV_copy_buffer 1
 typedef void ( *PFNGLXCOPYBUFFERSUBDATANVPROC) (Display *dpy, GLXContext readCtx, GLXContext writeCtx, GLenum readTarget, GLenum writeTarget, GLintptr readOffset, GLintptr writeOffset, GLsizeiptr size);