message: Fix `clean-sidebar` on sidebar updates
diff: @@ -2,7 +2,7 @@ import './clean-sidebar.css';
  import React from 'dom-chef';
  import select from 'select-dom';
  import features from '../libs/features';
  -import observeEl from '../libs/simplified-element-observer';
  +import onUpdatableContentUpdate from '../libs/on-updatable-content-update';
  import {isPR} from '../libs/page-detect';
  let canEditSidebar = false;
  @@ -76,7 +76,7 @@ function clean(): void {
  function init(): void {
  canEditSidebar = select.exists('.sidebar-labels .octicon-gear');
  clean();
  - observeEl('.discussion-sidebar', clean);
  + onUpdatableContentUpdate(select('#partial-discussion-sidebar')!, clean);
  }
  features.add({
  