lib: remove RUSAGE_T from struct thread

* thread.c: It's only temporarily used in thread_call() to calculate the
  diffs. Saves 80 bytes per copy.

Signed-off-by: Jorge Boncompte [DTI2] <jorge@dti2.net>
Signed-off-by: David Lamparter <equinox@opensourcerouting.org>
diff --git a/lib/thread.h b/lib/thread.h
index dfc51e2..56f4d07 100644
--- a/lib/thread.h
+++ b/lib/thread.h
@@ -77,7 +77,7 @@
     int fd;			/* file descriptor in case of read/write. */
     struct timeval sands;	/* rest of time sands value. */
   } u;
-  RUSAGE_T ru;			/* Indepth usage info.  */
+  struct timeval real;
   struct cpu_thread_history *hist; /* cache pointer to cpu_history */
   char* funcname;
 };