Disposes the System.Web.HttpApplication instance.
The HttpApplication.Request, HttpApplication.Response, HttpApplication.Session, and HttpApplication.Application properties are not available for use when the HttpApplication.Dispose method executes.
The HttpApplication.Dispose method calls the IHttpModule.Dispose method on each of the registered System.Web.Configuration.SystemWebSectionGroup.HttpModules in the application instance and raises the HttpApplication.Disposed event.