remove bind polyfill from new_branch_form.js

app/assets/javascripts/new_branch_form.js

 /* eslint-disable func-names, space-before-function-paren, no-var, one-var, prefer-rest-params, max-len, vars-on-top, wrap-iife, consistent-return, comma-dangle, one-var-declaration-per-line, quotes, no-return-assign, prefer-arrow-callback, prefer-template, no-shadow, no-else-return, max-len, object-shorthand */
 (function() {
-  var bind = function(fn, me) { return function() { return fn.apply(me, arguments); }; },
-    indexOf = [].indexOf || function(item) { for (var i = 0, l = this.length; i < l; i += 1) { if (i in this && this[i] === item) return i; } return -1; };
+  var indexOf = [].indexOf || function(item) { for (var i = 0, l = this.length; i < l; i += 1) { if (i in this && this[i] === item) return i; } return -1; };
 
   this.NewBranchForm = (function() {
     function NewBranchForm(form, availableRefs) {
-      this.validate = bind(this.validate, this);
+      this.validate = this.validate.bind(this);
       this.branchNameError = form.find('.js-branch-name-error');
       this.name = form.find('.js-branch-name');
       this.ref = form.find('#ref');