fix(aot): Unmount AlwaysOnTop to remove listeners (#2307)

react/features/always-on-top/index.js

@@ -8,3 +8,7 @@ ReactDOM.render(
     <AlwaysOnTop />,
     document.getElementById('react')
 );
+
+window.addEventListener('beforeunload', () => {
+    ReactDOM.unmountComponentAtNode(document.getElementById('react'));
+});