message: Simplify Memo::to_utf8 implementation
diff: @@ -123,13 +123,11 @@ impl Memo {
  pub fn to_utf8(&self) -> Option<Result<String, str::Utf8Error>> {
  // Check if it is a text or binary memo
  if self.0[0] < 0xF5 {
  - // Drop trailing zeroes
  - let mut data = &self.0[..];
  - while let Some((0, next)) = data.split_last() {
  - data = next;
  - }
  // Check if it is valid UTF8
  - Some(str::from_utf8(data).map(|memo| memo.to_owned()))
  + Some(str::from_utf8(&self.0).map(|memo| {
  + // Drop trailing zeroes
  + memo.trim_end_matches(char::from(0)).to_owned()
  + }))
  } else {
  None
  }
  