upgrade eslint config and remove workaround for implicit globals

we seem to have used eslint through codeclimate in the past, but that service seems no longer integrated, possibly due to no longer being free

js/privatebin.js

@@ -10,8 +10,6 @@
  * @namespace
  */
 
-// global Base64, DOMPurify, FileReader, baseX, bootstrap, history, navigator, prettyPrint, prettyPrintOne, showdown, kjua
-
 jQuery.fn.draghover = function() {
     'use strict';
     return this.each(function() {