Remove DOMContentLoaded Eventlisteners

Removing DOMContentLoaded Eventlisteners from
index files since the scripts
are embedded using the defer tag.

ee/app/assets/javascripts/pages/groups/billings/index.js

 import initSubscriptions from 'ee/billings';
 import PersistentUserCallout from '~/persistent_user_callout';
 
-document.addEventListener('DOMContentLoaded', () => {
-  PersistentUserCallout.factory(document.querySelector('.js-gold-trial-callout'));
-
-  initSubscriptions();
-});
+PersistentUserCallout.factory(document.querySelector('.js-gold-trial-callout'));
+initSubscriptions();

ee/app/assets/javascripts/pages/groups/epics/show/index.js

@@ -5,10 +5,8 @@ import ZenMode from '~/zen_mode';
 import '~/notes/index';
 import loadAwardsHandler from '~/awards_handler';
 
-document.addEventListener('DOMContentLoaded', () => {
-  new ZenMode(); // eslint-disable-line no-new
-  initEpicApp();
-  new ShortcutsEpic(); // eslint-disable-line no-new
-  new EpicTabs(); // eslint-disable-line no-new
-  loadAwardsHandler();
-});
+new ZenMode(); // eslint-disable-line no-new
+initEpicApp();
+new ShortcutsEpic(); // eslint-disable-line no-new
+new EpicTabs(); // eslint-disable-line no-new
+loadAwardsHandler();

ee/app/assets/javascripts/pages/groups/iterations/edit/index.js

 import { initIterationReport } from 'ee/iterations';
 import { Namespace } from 'ee/iterations/constants';
 
-document.addEventListener('DOMContentLoaded', () => {
-  initIterationReport({ namespaceType: Namespace.Group, initiallyEditing: true });
-});
+initIterationReport({ namespaceType: Namespace.Group, initiallyEditing: true });

ee/app/assets/javascripts/pages/groups/iterations/index.js

 import { initIterationsList } from 'ee/iterations';
 import { Namespace } from 'ee/iterations/constants';
 
-document.addEventListener('DOMContentLoaded', () => initIterationsList(Namespace.Group));
+initIterationsList(Namespace.Group);

ee/app/assets/javascripts/pages/groups/iterations/new/index.js

 import { initIterationForm } from 'ee/iterations';
 
-document.addEventListener('DOMContentLoaded', () => {
-  initIterationForm();
-});
+initIterationForm();

ee/app/assets/javascripts/pages/groups/iterations/show/index.js

 import { initIterationReport } from 'ee/iterations';
 import { Namespace } from 'ee/iterations/constants';
 
-document.addEventListener('DOMContentLoaded', () => {
-  initIterationReport({ namespaceType: Namespace.Group });
-});
+initIterationReport({ namespaceType: Namespace.Group });