WPF has removed PresentationUI ref assembly

[rladuca]

Follow on to: #3635

As a heads up, WPF has made the switch to GenAPI for reference assemblies. As such we've removed PresentationUI (or will be shortly) and handled the prior dangling reference from PresentationFramework's reference assembly.

This work is being done in dotnet/wpf#1057 and its associated internal PR.

@dagood This should be coming in Monday or Tuesday. I apologize for the late heads up and possible late flow, but we had issues with GenAPI code output that we had to manually overcome.

[rladuca]

We just got this in tonight. The next flow should see the removal of PresentationUI with no dangling references. Please let me know if anything goes awry.

Microsoft.DotNet.Wpf.DncEng 4.8.0-preview7.19324.35 should be the first package containing this change.

[dagood]

I applied a fixup (removing classification from PresentationUI) to dotnet/core-setup#6916 to unblock the PR.

[dagood]

PR was auto-merged successfully! Thanks for the heads up.