remove unnecessary indexOf polyfills

app/assets/javascripts/gl_dropdown.js

 /* eslint-disable func-names, space-before-function-paren, no-var, one-var, one-var-declaration-per-line, prefer-rest-params, max-len, vars-on-top, wrap-iife, no-unused-vars, quotes, no-shadow, no-cond-assign, prefer-arrow-callback, no-return-assign, no-else-return, camelcase, comma-dangle, no-lonely-if, guard-for-in, no-restricted-syntax, consistent-return, prefer-template, no-param-reassign, no-loop-func, no-mixed-operators */
 /* global fuzzaldrinPlus */
-var GitLabDropdown, GitLabDropdownFilter, GitLabDropdownRemote,
-  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 GitLabDropdown, GitLabDropdownFilter, GitLabDropdownRemote;
 GitLabDropdownFilter = (function() {
   var ARROW_KEY_CODES, BLUR_KEYCODES, HAS_VALUE_CLASS;
@@ -626,8 +625,8 @@ GitLabDropdown = (function() {
   };
   GitLabDropdown.prototype.highlightTextMatches = function(text, term) {
-    var occurrences;
-    occurrences = fuzzaldrinPlus.match(text, term);
+    const occurrences = fuzzaldrinPlus.match(text, term);
+    const indexOf = [].indexOf;
     return text.split('').map(function(character, i) {
       if (indexOf.call(occurrences, i) !== -1) {
         return "<b>" + character + "</b>";

app/assets/javascripts/merge_request_widget.js

@@ -7,8 +7,6 @@ import './smart_interval';
 import MiniPipelineGraph from './mini_pipeline_graph_dropdown';
 ((global) => {
-  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; };
-
   const DEPLOYMENT_TEMPLATE = `<div class="mr-widget-heading" id="<%- id %>">
        <div class="ci_widget ci-success">
          <%= ci_success_icon %>
@@ -258,7 +256,7 @@ import MiniPipelineGraph from './mini_pipeline_graph_dropdown';
       let stateClass = 'btn-danger';
       if (!hasCi) {
         stateClass = 'btn-create';
-      } else if (indexOf.call(allowed_states, state) !== -1) {
+      } else if (allowed_states.indexOf(state) !== -1) {
         switch (state) {
           case "failed":
           case "canceled":

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 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 = this.validate.bind(this);
@@ -94,6 +92,8 @@
     NewBranchForm.prototype.validate = function() {
       var errorMessage, errors, formatter, unique, validator;
+      const indexOf = [].indexOf;
+
       this.branchNameError.empty();
       unique = function(values, value) {
         if (indexOf.call(values, value) === -1) {