Revert "OpenGL: fix compilation / missing glXGetProcAddressARB"

This reverts commit 9abb97d0.

Sadly, this is not the right fix.

modules/video_output/xcb/glx.c

@@ -470,7 +470,7 @@ static void SwapBuffers (vlc_gl_t *gl)
 static void *GetProcAddress (vlc_gl_t *gl, const char *name)
 {
     (void)gl;
-#if defined(GLX_ARB_get_proc_address) && defined(GLX_GLXEXT_PROTOTYPES)
+#ifdef GLX_ARB_get_proc_address
     return glXGetProcAddressARB ((const GLubyte *)name);
 #else
     return NULL;