Enable no-unused-labels lint

I'm not sure why "esversion: 6" was at the top of the file. My best
guess is that whoever initially created it was using jshint, which says
"use 'esversion: 6'" if used to lint a file which contains ES6 code.
Even then, the proper syntax would be a comment.

public/scripts/RossAscends-mods.js

@@ -1,5 +1,3 @@
-esversion: 6
-
 import {
     Generate,
     characters,