Migrate W3cXsd2001 code to new open source code

[patridge]

Latest .NET doesn't recognize the namespace anymore.

using System.Runtime.Remoting.Metadata.W3cXsd2001;

Apparently, this code now exists in an open source repo.

https://github.com/microsoft/referencesource/blob/master/mscorlib/system/runtime/remoting/soapinteroptypes.cs