thread_pthread.c (native_sleep): do not clear unblock.arg

It is unnecessary to clear unblock.arg once unblock.func is
cleared, and unblock_function_clear in thread.c doesn't
touch it, either.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63724 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

thread_pthread.c

@@ -1069,7 +1069,6 @@ native_sleep(rb_thread_t *th, struct timespec *timeout_rel)
 		native_cond_timedwait(cond, lock, &timeout);
 	}
 	th->unblock.func = 0;
-	th->unblock.arg = 0;
 
 	rb_native_mutex_unlock(lock);
     }