Removed duplicate useEffect in dynamic-device-pixel-ratio docs (#515)

Author: WilliamSongLiu

documentation/docs/advanced-examples/dynamic-device-pixel-ratio.md

@@ -3,7 +3,7 @@
 In the following example, we'll render our Unity Application using a device pixel ratio which matches the device pixel ratio of the browser. We'll create an event listener using a media matcher which will update the device pixel ratio of the Unity Application when the device pixel ratio changes.
 
 ```jsx showLineNumbers title="App.jsx"
-import React, { useState, useEffect, useEffect } from "react";
+import React, { useState, useEffect } from "react";
 import { Unity, useUnityContext } from "react-unity-webgl";
 
 function App() {