Remove Darwin code from Xvnc

We don't build for that platform anyway, so this is just a remnant from
Xvfb.

unix/xserver/hw/vnc/xvnc.c

@@ -221,28 +221,6 @@ AbortDDX(enum ExitCode error)
     ddxGiveUp(error);
 }
 
-#ifdef __DARWIN__
-void
-DarwinHandleGUI(int argc, char *argv[])
-{
-}
-
-void GlxExtensionInit();
-void GlxWrapInitVisuals(void *procPtr);
-
-void
-DarwinGlxExtensionInit()
-{
-    GlxExtensionInit();
-}
-
-void
-DarwinGlxWrapInitVisuals(void *procPtr)
-{
-    GlxWrapInitVisuals(procPtr);
-}
-#endif
-
 void
 OsVendorInit(void)
 {