Remove legacy source-build switches

[mmitche]

To double check:

• [ ] The right tests are in and the right validation has happened. Guidance: https://github.com/dotnet/arcade/blob/main/Documentation/Validation.md

[mmitche]

Resolves https://github.com/dotnet/source-build/issues/4182

[MichaelSimons]

The scope of https://github.com/dotnet/source-build/issues/4182 is not clear. What is tracking the removal of ExcludeFromSourceBuild? I don't see any other issue in https://github.com/dotnet/source-build/issues/2975 that would include this besides https://github.com/dotnet/source-build/issues/4182. I am asking if https://github.com/dotnet/source-build/issues/4182 should remain open until this is done?

[mmitche]

ExcludeFromSourceBuild is tracked by https://github.com/dotnet/source-build/issues/4182. It should be gone with this PR.

[mmitche]

I still see a couple remaining usages so holding off on merging this.