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/uuid.h b/aos/uuid.h
index 371eb6d..8dd93d4 100644
--- a/aos/uuid.h
+++ b/aos/uuid.h
@@ -9,8 +9,6 @@
 #include "absl/types/span.h"
 #include "flatbuffers/flatbuffers.h"
 
-#include "aos/thread_local.h"
-
 namespace aos {
 
 // Class to generate and hold a UUID.
@@ -76,7 +74,7 @@
   // Be careful using this. It's mostly useful for low-level tracing of UUIDs
   // through the system.
   const char *thread_local_string() const {
-    AOS_THREAD_LOCAL char buffer[kStringSize + 1];
+    thread_local char buffer[kStringSize + 1];
     CopyTo(buffer);
     return buffer;
   }