Simplify handling of negative numbers in add(…) function.

Author: nathansmith

ANSWERS.md

@@ -660,7 +660,6 @@ Joking aside though, if you're a job applicant skimming these answers so that yo
  // Undefined, set in the loop
  var value;
  var value_split;
- var is_negative;
  var integer;
  var decimal;