[.NET 9] Remove UsingToolMicrosoftNetILLinkTasks switch

[ViktorHofer]

Blocked by dotnet/runtime#91468

This shouldn't be merged into main as long as Arcade targets .NET 8.

Runtime was the only consumer of that switch and we now use the live built asset instead. Also, the linker is now in-built into the .NET SDK and doesn't need to be referenced explicitly anymore.

To double check:

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

[ViktorHofer]

@mmitche when should we expect Arcade to branch-off so that we can get this change merged?

[mmitche]

@mmitche when should we expect Arcade to branch-off so that we can get this change merged?

I may be recalling incorrectly, but I think @dkurepa was going to work on this sometime soon?

[dkurepa]

I don't think we talked about this, but I could work on this

[mmitche]

I don't think we talked about this, but I could work on this

Maybe that was someone else. @tkapin did I talk to you about this?

[tkapin]

@mmitche - I don't this so, this doesn't ring a bell.

[ViktorHofer]

@sbomer can you please review? This was a feature that only dotnet/runtime used.

[sbomer]

LGTM, thanks! We should probably hold off on merging it until dotnet/runtime#91468 is ready.