Ensure no management api for v12 (#14197)

* Remove management api

* Remove actual files

tests/Umbraco.Tests.UnitTests/Umbraco.Core/ReflectionUtilitiesTests.cs

@@ -1,7 +1,6 @@
 // Copyright (c) Umbraco.
 // See LICENSE for more details.
 
-using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Reflection;