message: Unregister metrics on drop.
diff: @@ -57,5 +57,6 @@ impl Drop for Metrics {
  unregister_metric!(self.registry, self.found_in_storage);
  unregister_metric!(self.registry, self.found_on_peer);
  unregister_metric!(self.registry, self.timeouts);
  + unregister_metric!(self.registry, self.fetch_total);
  }
  }
  