Removing duplicate IIFE example

Author: bikkimahato

challenges/functions-concepts.md

@@ -263,12 +263,6 @@ Hoisting was thought up as a general way of thinking about how execution context
 })();
 ```
 
-```js
-(function IIFE() {
-  console.log("I am an Immediately invoked function");
-})();
-```
-
 ```js
 +(function IIFE() {
   console.log("I am an Immediately invoked function");