dotnet-svcutil: Reduce FrameworkFork/System.Web.Services by using System.Web.Services.Description package

There is a framework fork under `src/dotnet-svcutil/lib/src/FrameworkFork/System.Web.Services/...`

A shipped NuGet package (System.Web.Services.Description) exists and provides a standalone subset of this functionality. This suggests some of the forked code may be replaceable by the package.