Revert #124 and #135 (#139)

This seems to be causing a lot of weirdness, presumably because there's
another missing thing like in #135, but I don't know what it might be and
it feels like it might take a while to find. Backing these changes out
to fix develop while we sort it out.

Fixes https://github.com/element-hq/element-web/issues/28179

src/stores/right-panel/RightPanelStore.ts

@@ -403,6 +403,7 @@ export default class RightPanelStore extends ReadyWatchingStore {
     public static get instance(): RightPanelStore {
         if (!this.internalInstance) {
             this.internalInstance = new RightPanelStore();
+            this.internalInstance.start();
         }
         return this.internalInstance;
     }