fix: remove unused useState import in lifecycle-of-reactive-effects (#8483)

The ChatRoom.js sandpack in the "Fix a connection switch" challenge
imports useState but only uses useEffect. Remove the unused import
to avoid confusing learners.

Fixes #8231

Author: jahanzaib-iqbal-dev

src/content/learn/lifecycle-of-reactive-effects.md

@@ -1375,7 +1375,7 @@ export default function App() {
 ```
 
 ```js {expectedErrors: {'react-compiler': [8]}} src/ChatRoom.js active
-import { useState, useEffect } from 'react';
+import { useEffect } from 'react';
 
 export default function ChatRoom({ roomId, createConnection }) {
   useEffect(() => {