Remove configuration preprocessor symbols 'THREAD'

and 'THREAD_SAFE_CLIENT'.
  
As of MySQL 5.5, we no longer support non-threaded
builds.   This patch removes all references to the
obsolete THREAD and THREAD_SAFE_CLIENT preprocessor
symbols.  These were used to distinguish between
threaded and non-threaded builds.

mysys/my_pthread.c

@@ -18,7 +18,6 @@
 #define DONT_REMAP_PTHREAD_FUNCTIONS
 
 #include "mysys_priv.h"
-#ifdef THREAD
 #include <signal.h>
 #include <m_string.h>
 #include <thr_alarm.h>
@@ -468,4 +467,3 @@ int pthread_dummy(int ret)
 {
   return ret;
 }
-#endif /* THREAD */