Docs: unused variable removed

The `const ctx` declaration in `loop` shadows the `let ctx` declaration in the outer scope. 
This change removes the outer declaration.

site/content/examples/05-bindings/10-bind-this/App.svelte

@@ -2,7 +2,6 @@
 	import { onMount } from 'svelte';
 
 	let canvas;
-	let ctx;
 	let running = false;
 
 	const r = Math.random();