Avoid duplicate output.

The output from the btrfs command is better, don't duplicate the output.

roles/debian_server/files/btrfs-scrub

@@ -14,6 +14,5 @@ do
         echo "Scrub already running on $mp, skipping." >&2
         continue
     fi
-    btrfs scrub start "$mp"
-    echo "Started scrub on $mp." >&2
+    btrfs scrub start "$mp" >&2
 done