message: fix clippy
  Revert previous changes that handled safely converting between u64 and
  usize. Instead, use unwrap() since we are not expecting these to happen.
diff: @@ -301,25 +301,18 @@ impl TxBuffer {
  pub fn next_bytes(&self, _mode: TxMode) -> Option<(u64, &[u8])> {
  let (start, maybe_len) = self.ranges.first_unmarked_range();
  - match (usize::try_from(start), usize::try_from(self.retired)) {
  - (Ok(s), Ok(retired)) => {
  - if s == retired + self.buffered() {
  +
  + if start == self.retired + u64::try_from(self.buffered()).unwrap() {
  return None;
  }
  - debug_assert!(s >= retired);
  - let buff_off = s - retired;
  - // Unwrap is safe here because we checked if maybe_len.is_some() beforehand
  - if maybe_len.is_some() {
  - if let Ok(len) = usize::try_from(maybe_len.unwrap()) {
  - Some((start, &self.send_buf[buff_off..buff_off + len]))
  - } else {
  - Some((start, &self.send_buf[buff_off..]))
  - }
  - } else {
  - Some((start, &self.send_buf[buff_off..]))
  - }
  - }
  - _ => None,
  +
  + let buff_off = usize::try_from(start - self.retired).unwrap();
  + match maybe_len {
  + Some(len) => Some((
  + start,
  + &self.send_buf[buff_off..buff_off + usize::try_from(len).unwrap()],
  + )),
  + None => Some((start, &self.send_buf[buff_off..])),
  }
  }
  