input: Write a function to create a REST API in Python that allows to delete an item from a list.
  assert delete_item("Apple")==json.dumps({"message": "Item successfully deleted."})
  assert delete_item("Grape")==json.dumps({"message": "Item not found."})
output: def delete_item(item):
      items = ["Apple", "Banana", "Orange"]
      if item in items:
          items.remove(item)
          return json.dumps({"message": "Item successfully deleted."})
      else:
          return json.dumps({"message": "Item not found."})