Moved private USER definitions to a new user_private.h header, and
removed the global user.h.

diff --git a/dlls/user/hook16.c b/dlls/user/hook16.c
index 8bcef5c..073d91df 100644
--- a/dlls/user/hook16.c
+++ b/dlls/user/hook16.c
@@ -30,6 +30,7 @@
 #include "wine/winuser16.h"
 #include "message.h"
 #include "win.h"
+#include "user_private.h"
 #include "winproc.h"
 #include "wine/debug.h"