input: Write a function to delete an item from a list. If the item is found in the list, it should be removed and a message "Item successfully deleted." should be returned. If the item is not found, a message "Item not found." should be returned. The list should be initialized with ["Apple", "Banana", "Orange"].
  assert delete_item(["Apple", "Banana", "Orange"], "Banana")=={"message": "Item successfully deleted."}
  assert delete_item(["Apple", "Banana", "Orange"], "Grape")=={"message": "Item not found."}
  assert delete_item(["Apple", "Orange"], "Apple")=={"message": "Item successfully deleted."}
  assert delete_item([], "Banana")=={"message": "Item not found."}
output: def delete_item(lst, item):
      if item in lst:
          lst.remove(item)
          return {"message": "Item successfully deleted."}
      else:
          return {"message": "Item not found."}