unused React import for hooks example (#1979)

I believe this was just from a copy/paste from the JSX example

content/docs/hooks-custom.md

@@ -74,7 +74,7 @@ When we want to share logic between two JavaScript functions, we extract it to a
 **A custom Hook is a JavaScript function whose name starts with "`use`" and that may call other Hooks.** For example, `useFriendStatus` below is our first custom Hook:
 
 ```js{3}
-import React, { useState, useEffect } from 'react';
+import { useState, useEffect } from 'react';
 
 function useFriendStatus(friendID) {
   const [isOnline, setIsOnline] = useState(null);