Respond to sourcelink being bundled in the SDK

[MichaelSimons]

SourceLink is now be bundled in with the SDK - dotnet/sdk#31632. This has an impact on source-build that needs to be reacted to. SourceLink will no longer be required to be build as one of the source-build toolset repos. The SourceLink used by the build will now come from the SDK used to build the product. The sourcelink repo can now be treated as a normal product repo which the SDK has a dependency on.

[MichaelSimons]

[Triage] This work will be blocked on the cleanup work to remove the sourcelink version.details dependencies from the product repos.

[MichaelSimons]

Closing as completed. #3551 tracks cleaning up the sourcelink dependencies.