message: Use flush combinator
diff: @@ -23,9 +23,7 @@ where
  frontend::cancel_request(process_id, secret_key, &mut buf);
  stream.write_all(&buf).await.map_err(Error::io)?;
  - future::poll_fn(|cx| Pin::new(&mut stream).poll_flush(cx))
  - .await
  - .map_err(Error::io)?;
  + stream.flush().await.map_err(Error::io)?;
  future::poll_fn(|cx| Pin::new(&mut stream).poll_shutdown(cx))
  .await
  .map_err(Error::io)?;
  