input: Write a function to implement a REST API endpoint in Python that allows the deletion of an item from a list. The function should return a JSON response indicating the success or failure of the deletion operation. The list of items initially contains ["Apple", "Banana", "Orange"]. If the item to be deleted is in the list, it should be removed and the response should indicate success; otherwise, it should indicate that the item was not found.
  
  from flask import Flask, request
  import json
  
  app = Flask(__name__)
  items = ["Apple", "Banana", "Orange"]
  
  @app.route('/items', methods=["GET"])
  def get_items():
   return json.dumps(items)
  
  @app.route('/items/<item>', methods=["DELETE"])
  def delete_item(item):
   if item in items:
    items.remove(item)
    message = "Item successfully deleted."
   else:
    message = "Item not found."
   return json.dumps({"message": message})
  
  assert delete_item("Banana") == json.dumps({"message": "Item successfully deleted."})
  assert delete_item("Grape") == json.dumps({"message": "Item not found."})
  assert delete_item("Apple") == json.dumps({"message": "Item successfully deleted."})
  assert delete_item("Orange") == json.dumps({"message": "Item successfully deleted."})
  assert delete_item("Banana") == json.dumps({"message": "Item not found."})
output: if item in items:
   items.remove(item)
   message = "Item successfully deleted."
  else:
   message = "Item not found."
  return json.dumps({"message": message})