Removed unnecessary includes.

diff --git a/windows/user.c b/windows/user.c
index 9380233..32441f5 100644
--- a/windows/user.c
+++ b/windows/user.c
@@ -11,6 +11,7 @@
 #include "windef.h"
 #include "wingdi.h"
 #include "winuser.h"
+#include "wine/winuser16.h"
 #include "heap.h"
 #include "user.h"
 #include "win.h"
@@ -20,7 +21,6 @@
 #include "message.h"
 #include "miscemu.h"
 #include "sysmetrics.h"
-#include "callback.h"
 #include "local.h"
 #include "module.h"
 #include "debugtools.h"