remove OSX specific fix where CLOCK_REALTIME is not defined.

It has been properly fixed in
http://mail-index.netbsd.org/source-changes/2010/03/26/msg008200.html

tools/compat/sys/time.h

@@ -1,11 +0,0 @@
-/*	$NetBSD: time.h,v 1.1 2010/03/26 07:16:12 cegger Exp $	*/
-
-#if (defined(__APPLE__) && defined(__MACH__)) && !defined(__darwin__)
-# define __darwin__     1
-#endif
-
-#ifdef __darwin__
-#define CLOCK_REALTIME	0	/* XXX Keep this in sync with our sys/time.h */
-#endif
-
-#include_next <sys/time.h>