message: refactor(examples): remove lifetime workaround in send_file example
  The lifetime workaround is no longer required due to changes in
  rustc. This removes the line and comment from the example.
diff: @@ -61,13 +61,11 @@ fn internal_server_error() -> Response<Body> {
  .unwrap()
  }
  -async fn simple_file_send(f: &str) -> Result<Response<Body>> {
  +async fn simple_file_send(filename: &str) -> Result<Response<Body>> {
  // Serve a file by asynchronously reading it entirely into memory.
  // Uses tokio_fs to open file asynchronously, then tokio::io::AsyncReadExt
  // to read into memory asynchronously.
  - let filename = f.to_string(); // we need to copy for lifetime issues
  -
  if let Ok(mut file) = File::open(filename).await {
  let mut buf = Vec::new();
  if let Ok(_) = file.read_to_end(&mut buf).await {
  