Add a comment header to explain why this is still here

src/Compilers/Core/Portable/Interop/IVsSQM.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+// WARNING: THIS FILE IS BEING CONSUMED THROUGH INTERNALSVISIBLETO
+// BY THE RULSET EDITOR. Until you fix that, do not delete this file.
+
 ///////////////////////////////////////////////////////////////////////////////
 //
 //