Remove work around for old glibc.

properties.m

@@ -4,7 +4,7 @@
 #include <assert.h>
 #include <stdlib.h>
 #include <string.h>
-#include "unistd.h"
+#include <unistd.h>
 #include "class.h"
 #include "properties.h"
 #include "spinlock.h"

unistd.h

@@ -1,10 +0,0 @@
-/* See http://llvm.org/bugs/show_bug.cgi?id=4746 */
-#ifdef __block
-#	undef __block
-#	include_next "unistd.h"
-#	define __block __attribute__((__blocks__(byref)))
-#else
-#	if __has_include_next("unitstd.h")
-#		include_next "unistd.h"
-#	endif
-#endif