docs: fix the payload in event-binding sample code (#30429)

after reading the context. there are  some clues to infer the payload should be the `item`, not `item.name`.
1.  EventEmitter<Item>.
2.  the desc say that:
The component defines a deleteRequest property that returns an EventEmitter. When the user clicks delete, the component invokes the delete() method, telling the EventEmitter to emit an **Item** object.

PR Close #30429

aio/content/examples/event-binding/src/app/item-detail/item-detail.component.ts

@@ -21,7 +21,7 @@ export class ItemDetailComponent {
   @Output() deleteRequest = new EventEmitter<Item>();
 
   delete() {
-    this.deleteRequest.emit(this.item.name);
+    this.deleteRequest.emit(this.item);
     this.displayNone = this.displayNone ? '' : 'none';
     this.lineThrough = this.lineThrough ? '' : 'line-through';
   }