fix compile error

Author: Oceania2018

src/Infrastructure/BotSharp.OpenAPI/BotSharpOpenApiExtensions.cs

@@ -12,7 +12,6 @@
 using BotSharp.OpenAPI.BackgroundServices;
 using System.Text.Json.Serialization;
 using Microsoft.AspNetCore.Authentication;
-using Microsoft.OpenApi.Models;
 
 namespace BotSharp.OpenAPI;