Removed unused parameter

Closes #3810

modules/angular2/docs/core/02_directives.md

@@ -74,7 +74,7 @@ class Form {                 | Directive controller class, instantiated
                              | when CSS matches.
   text:string;               | text property on the Directive Controller.
                              |
-  show(event) {              | Show method which implements the show action.
+  show() {                   | Show method which implements the show action.
     console.log(this.text);  |
   }
 }