Remove old thread_local.h

This was to work around a clang 9.0.0 bug.  We are on clang 13.  Make
things simpler by removing it.

Change-Id: I4bad16270795bb82b8c498146a4bf7388565a1c7
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/aos/libc/aos_strerror.cc b/aos/libc/aos_strerror.cc
index 8c087a8..9d270c0 100644
--- a/aos/libc/aos_strerror.cc
+++ b/aos/libc/aos_strerror.cc
@@ -6,8 +6,6 @@
 #include <cstdio>
 #include <cstring>
 
-#include "aos/thread_local.h"
-
 // This code uses an overloaded function to handle the result from either
 // version of strerror_r correctly without needing a way to get the choice out
 // of the compiler/glibc/whatever explicitly.
@@ -41,7 +39,7 @@
 }  // namespace
 
 const char *aos_strerror(int error) {
-  AOS_THREAD_LOCAL char buffer[kBufferSize];
+  thread_local char buffer[kBufferSize];
 
   // Call the overload for whichever version we're using.
   return aos_strerror_handle_result(