message: silence a warning about unused variable
diff: @@ -249,7 +249,8 @@ impl DelegationState {
  ));
  }
  - if let Some(old) = new_state.register_stake_key(reg.data.stake_key_id.clone()) {
  + if let Some(_original) = new_state.register_stake_key(reg.data.stake_key_id.clone())
  + {
  // FIXME: error stake key already registered
  return Err(Error::new_(
  ErrorKind::InvalidBlockMessage,
  