dedupe: remove rb_lock when done

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/t/dedupe.c b/t/dedupe.c
index bd8214c..16c1748 100644
--- a/t/dedupe.c
+++ b/t/dedupe.c
@@ -520,6 +520,7 @@
 
 	iter_rb_tree();
 
+	fio_mutex_remove(rb_lock);
 	scleanup();
 	return ret;
 }