dxerr9: Exclude unused header

[Andrew Talbot]

Changelog:
    dxerr9: Exclude unused header.

diff -urN a/dlls/dxerr9/dxerr9.c b/dlls/dxerr9/dxerr9.c
--- a/dlls/dxerr9/dxerr9.c	2006-10-24 19:41:28.000000000 +0100
+++ b/dlls/dxerr9/dxerr9.c	2007-05-02 19:31:14.000000000 +0100
@@ -25,7 +25,6 @@
 #include "winbase.h"
 #include "wingdi.h"
 #include "winuser.h"
-#include "winnls.h"
 
 #include "mmsystem.h"
 #include "dmerror.h"