Remove incorrect line in "IndexPOST" action

The navigation screen doesn't show any part other than "MenuPart".
Calling "UpdateEditorModel" on all the content items in the POST
action causes data loss (slug, title, tags, etc..) when clicking
the "Update All" button.

--HG--
branch : dev

src/Orchard.Web/Core/Navigation/Controllers/AdminController.cs

@@ -52,8 +52,6 @@ namespace Orchard.Core.Navigation.Controllers {
                 menuPart.MenuPosition = menuItemEntry.MenuItem.Position;
                 if (menuPart.Is<MenuItemPart>())
                     menuPart.As<MenuItemPart>().Url = menuItemEntry.MenuItem.Url;
-
-                _services.ContentManager.UpdateEditorModel(menuPart, this);
             }
 
             return RedirectToAction("Index");