message: Remove deprecated impls for IoError
diff: @@ -36,23 +36,7 @@ impl fmt::Display for IoError {
  }
  }
  -impl Error for IoError {
  - fn description(&self) -> &str {
  - match *self {
  - IoError::Io(ref err) => err.description(),
  - IoError::BadMatrixMarketFile => "bad matrix market file",
  - IoError::UnsupportedMatrixMarketFormat => "unsupported format",
  - }
  - }
  -
  - fn cause(&self) -> Option<&dyn Error> {
  - match *self {
  - IoError::Io(ref err) => Some(err),
  - IoError::BadMatrixMarketFile => None,
  - IoError::UnsupportedMatrixMarketFormat => None,
  - }
  - }
  -}
  +impl Error for IoError {}
  impl From<io::Error> for IoError {
  fn from(err: io::Error) -> IoError {
  