Fix initialization of a few scripts

ee/app/assets/javascripts/pages/admin/emails/show/index.js

 import AdminEmailSelect from './admin_email_select';
 
-document.addEventListener('DOMContentLoaded', () => new AdminEmailSelect());
+document.addEventListener('DOMContentLoaded', () => {
+  AdminEmailSelect();
+});

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

 import $ from 'jquery';
-import DependencyProxy from 'ee/dependency_proxy';
+import initDependencyProxy from 'ee/dependency_proxy';
 
-document.addEventListener('DOMContentLoaded', () => new DependencyProxy());
+document.addEventListener('DOMContentLoaded', () => {
+  initDependencyProxy();
+});
 
 document.addEventListener('DOMContentLoaded', () => {
   const form = document.querySelector('form.edit_dependency_proxy_group_setting');

ee/app/assets/javascripts/pages/projects/issues/form.js

-import EpicsSelect from 'ee/vue_shared/components/sidebar/epics_select/epics_select_bundle';
+import initEpicsSelect from 'ee/vue_shared/components/sidebar/epics_select/epics_select_bundle';
 import WeightSelect from 'ee/weight_select';
 import initForm from '~/pages/projects/issues/form';
 
 export default () => {
-  // eslint-disable-next-line no-new
-  new EpicsSelect();
+  initEpicsSelect();
   // eslint-disable-next-line no-new
   new WeightSelect();
   initForm();