Revert componentDidMount changes on breadcrumbs

Fixes https://github.com/vector-im/riot-web/issues/12990

Regressed in https://github.com/matrix-org/matrix-react-sdk/pull/4313

src/components/structures/LeftPanel.js

@@ -44,7 +44,8 @@ const LeftPanel = createReactClass({
         };
     },
 
-    componentDidMount: function() {
+    // TODO: [REACT-WARNING] Move this to constructor
+    UNSAFE_componentWillMount: function() {
         this.focusedElement = null;
 
         this._breadcrumbsWatcherRef = SettingsStore.watchSetting(

src/components/views/rooms/RoomBreadcrumbs.js

@@ -49,7 +49,8 @@ export default class RoomBreadcrumbs extends React.Component {
         this._scroller = createRef();
     }
 
-    componentDidMount() {
+    // TODO: [REACT-WARNING] Move this to constructor
+    UNSAFE_componentWillMount() {
         this._dispatcherRef = dis.register(this.onAction);
 
         const storedRooms = SettingsStore.getValue("breadcrumb_rooms");