xmesa: deprecate the "XMesa" interface

Move the include/GL/xmesa*.h files to src/mesa/drivers/x11/ so they're no
longer considered public.

src/mesa/drivers/x11/fakeglx.c

@@ -42,7 +42,6 @@
 
 #include "glxheader.h"
 #include "glxapi.h"
-#include "GL/xmesa.h"
 #include "main/context.h"
 #include "main/config.h"
 #include "main/macros.h"

src/mesa/drivers/x11/xm_api.c

@@ -63,7 +63,6 @@
 #endif
 
 #include "glxheader.h"
-#include "GL/xmesa.h"
 #include "xmesaP.h"
 #include "main/context.h"
 #include "main/extensions.h"

src/mesa/drivers/x11/xm_buffer.c

@@ -30,7 +30,6 @@
 
 
 #include "glxheader.h"
-#include "GL/xmesa.h"
 #include "xmesaP.h"
 #include "main/imports.h"
 #include "main/framebuffer.h"

src/mesa/drivers/x11/xmesaP.h

@@ -27,7 +27,7 @@
 #define XMESAP_H
 
 
-#include "GL/xmesa.h"
+#include "xmesa.h"
 #include "main/mtypes.h"
 #if defined(FX)
 #include "GL/fxmesa.h"