message: [language][move] Replace some unreachable error handling code
  The parse_value function is only called after checking that the
  next token is one of the things that it handles, so there is
  no need to check again inside the function.
  Closes:
  Approved by: tzakian
diff: @@ -387,25 +387,26 @@ fn parse_bind_list<'input>(tokens: &mut Lexer<'input>) -> Result<BindList, Error
  // | <U64>
  fn parse_value<'input>(tokens: &mut Lexer<'input>) -> Result<Value, Error> {
  let start_loc = tokens.start_loc();
  - let val = token_match!(tokens.peek(), tokens.file_name(), start_loc, tokens.content(), {
  + let val = match tokens.peek() {
  Tok::AddressValue => {
  let addr = parse_address(tokens)?;
  Value_::Address(addr)
  - },
  + }
  Tok::True => {
  tokens.advance()?;
  Value_::Bool(true)
  - },
  + }
  Tok::False => {
  tokens.advance()?;
  Value_::Bool(false)
  - },
  + }
  Tok::U64Value => {
  let i = u64::from_str(tokens.content()).unwrap();
  tokens.advance()?;
  Value_::U64(i)
  }
  - });
  + _ => unreachable!("parse_value called with invalid token"),
  + };
  let end_loc = tokens.previous_end_loc();
  Ok(spanned(tokens.file_name(), start_loc, end_loc, val))
  }
  