Remove LegacyElementMixin everywhere

Change-Id: I0d8ba8d09d7b12fcfe8adc27df90ffa8bfd8c0fb
diff --git a/polygerrit-ui/app/elements/change-list/gr-change-list-view/gr-change-list-view.ts b/polygerrit-ui/app/elements/change-list/gr-change-list-view/gr-change-list-view.ts
index da84b45..8ce00f2 100644
--- a/polygerrit-ui/app/elements/change-list/gr-change-list-view/gr-change-list-view.ts
+++ b/polygerrit-ui/app/elements/change-list/gr-change-list-view/gr-change-list-view.ts
@@ -20,7 +20,6 @@
 import '../gr-repo-header/gr-repo-header';
 import '../gr-user-header/gr-user-header';
 import '../../../styles/shared-styles';
-import {LegacyElementMixin} from '@polymer/polymer/lib/legacy/legacy-element-mixin';
 import {PolymerElement} from '@polymer/polymer/polymer-element';
 import {htmlTemplate} from './gr-change-list-view_html';
 import {page} from '../../../utils/page-wrapper-utils';
@@ -61,7 +60,7 @@
 }
 
 @customElement('gr-change-list-view')
-export class GrChangeListView extends LegacyElementMixin(PolymerElement) {
+export class GrChangeListView extends PolymerElement {
   static get template() {
     return htmlTemplate;
   }