Examples: Cleanup. (#32057)

examples/webgpu_tonemapping.html

@@ -46,7 +46,7 @@
 			import { HDRLoader } from 'three/addons/loaders/HDRLoader.js';
 
 			let renderer, scene, camera, controls;
-			let gui = null;
+			let gui;
 
 			const params = {
 				exposure: 1.0,