utils: remove reference to yams from unified SPM project

[compnerd]

Remove the reference to Yams from the unified workspace as this dependency has been removed.

[compnerd]

@swift-ci please smoke test

[etcwilde]

@dschaefer2, I know Yams has been removed, but I'm not familiar with the "SwiftPM Unified Build".
@hamishknight, is this used by your Xcode integration scripts at all?

[etcwilde]

I think that this is fine, but would like reviews from folks affected by changes to this file to chime in as well.

[dschaefer2]

@dschaefer2, I know Yams has been removed, but I'm not familiar with the "SwiftPM Unified Build".

Me neither. Sounds fine. I don't know anywhere this is used.

[bnbarham]

Me neither. Sounds fine. I don't know anywhere this is used.

It's used by all the downstream packages during a toolchain build outside of Windows - everything builds into a "unified" root so that we don't needlessly rebuild dependencies every time. For Windows it's only used by the projects that build or test with SwiftPM (which is a fairly small set). There's no reason for Yams to be in there still.