fix type_traits for OSX

we are already using -std=c++11 -stdlib=libc++

Author: rogerwang

src/util.h

@@ -12,7 +12,7 @@
 #include <stdlib.h>
 
 // OSX 10.9 defaults to libc++ which provides a C++11 <type_traits> header.
-#if defined(__APPLE__) && __ENVIRONMENT_MAC_OS_X_VERSION_MIN_REQUIRED__ < 1090
+#if 0
 #define USE_TR1_TYPE_TRAITS
 #endif