Remove viewLoaded callback comment

This removes the comment about the `viewLoaded` callback since it refers
to upgrade instructions.

extensions/ql-vscode/src/view/webview.tsx

@@ -28,7 +28,6 @@ const render = () => {
 
   const root = createRoot(element);
   root.render(
-    // Post a message to the extension when fully loaded. See https://github.com/reactwg/react-18/discussions/5 ("What about the render callback?")
     <div ref={() => vscode.postMessage({ t: "viewLoaded", viewName })}>
       {view.component}
     </div>,