Don't use malloc.h header on OpenBSD.

--- win/jtp/jtp_keys.c.orig	Tue Nov 18 05:32:43 2014
+++ win/jtp/jtp_keys.c	Tue Nov 18 05:32:50 2014
@@ -2,7 +2,6 @@
 /* Copyright (c) Jaakko Peltonen, 2001				  */
 /* NetHack may be freely redistributed.  See license for details. */
 
-#include <malloc.h>
 #include "hack.h"
 #include "jtp_keys.h"
 
