Remove context.done for async js func

Author: mhoeger

articles/azure-functions/functions-bindings-warmup.md

@@ -128,7 +128,6 @@ Here's the JavaScript code:
 ```javascript
 module.exports = async function (context, warmupContext) {
     context.log('Function App instance is warm 🌞🌞🌞');
-    context.done();
 };
 ```