Consider bringing back "unlikely to service" packages so that we have a place to build them

Here's an interesting case for maintenance-packages: https://github.com/dotnet/runtime/issues/54341

Right now we don't build many of these packages any more because they no longer contain serviceable implementations - just facades / not-supported assemblies / reference assemblies. We could bring them back in maintenance-packages just to keep them building and update dependencies.

I think for this to be worthwhile we'd need to do it holistically and have enough customer value in doing so to warrant the work.