.NET Core 2.0 reached EOL last year. This removes multi-targeting our test projects and test assets to only use .NET Core 2.1 and .NET Framework 4.6.1.
- Stop producing the 'Universe' lineup package
- Removes all PackageLineup code
- Use full msbuild on Windows
- Fix invalid reference to internal.aspnetcore.sdk in 2.1.x
- Fix shared folder references for PackageArchive task.