input: Write a function to create a REST API in Python using Flask that allows the deletion of an item from a predefined list. The function should return a message indicating whether the deletion was successful or if the item was not found. The API should have a route for retrieving the list and a route for deleting a specific item.
  assert delete_item("Apple")=={"message": "Item successfully deleted."}
  assert delete_item("Grape")=={"message": "Item not found."}
  assert get_items()==["Banana", "Orange"]
output: def delete_item(item):
      global items
      if item in items:
          items.remove(item)
          return {"message": "Item successfully deleted."}
      else:
          return {"message": "Item not found."}
  
  def get_items():
      global items
      return items
  
  items = ["Apple", "Banana", "Orange"]