Revert 136389 - Enable system trace clock use on chrome os.

base/time_posix.cc

Index: base/time_posix.cc
===================================================================
--- base/time_posix.cc	(revision 136396)
+++ base/time_posix.cc	(working copy)
@@ -24,12 +24,6 @@
 #if defined(OS_ANDROID)
 #define _POSIX_MONOTONIC_CLOCK 1
 #endif
-#if defined(OS_CHROMEOS)
-// Force definition of the system trace clock; it is a chromeos-only api
-// at the moment and surfacing it in the right place requires mucking
-// with glibc et al.
-#define CLOCK_SYSTEM_TRACE 11
-#endif
 
 struct timespec TimeDelta::ToTimeSpec() const {
   int64 microseconds = InMicroseconds();