Xnest: use authorative declarations from X11/XKBlib.h

Better use the headers from the library we're linking against,
instead of having our own private declarations.

Signed-off-by: Enrico Weigelt, metux IT consult <info@metux.net>
Part-of: <https://gitlab.freedesktop.org/xorg/xserver/-/merge_requests/1842>

hw/xnest/Keyboard.c

@@ -36,28 +36,12 @@ is" without express or implied warranty.
 #include "Args.h"
 #include "Events.h"
 
+// must come after Xnest.h, because of trickery to avoid name clash
+#include <X11/XKBlib.h>
 #include <X11/extensions/XKB.h>
+
 #include "xkbsrv.h"
 
-extern Bool
- XkbQueryExtension(Display * /* dpy */ ,
-                   int * /* opcodeReturn */ ,
-                   int * /* eventBaseReturn */ ,
-                   int * /* errorBaseReturn */ ,
-                   int * /* majorRtrn */ ,
-                   int *        /* minorRtrn */
-    );
-
-extern XkbDescPtr XkbGetKeyboard(Display * /* dpy */ ,
-                                 unsigned int /* which */ ,
-                                 unsigned int   /* deviceSpec */
-    );
-
-extern Status XkbGetControls(Display * /* dpy */ ,
-                             unsigned long /* which */ ,
-                             XkbDescPtr /* desc */
-    );
-
 DeviceIntPtr xnestKeyboardDevice = NULL;
 
 void