Remove CPD to Microsoft.Private.Winforms temporarily

[vatsan-madhavan]

Porting #534 to master.

Removes CPD to Microsoft.Private.Winforms temporarily, until updated C++/CLI toolset becomes available (see related issues below).

This will help ensure that WindowsDesktop apps (i.e., WPF and WinForms apps) built out of dotnet/windowsdesktop and targeting the shared sdk are able to find and load the runtime bundled with the SDK itself.

The downside is that the runtime that is bundled with the SDK is not the runtime (i.e., the ref-assemblies corresponding to the runtime) that was used to build WinForms and WPF binaries. This is what the CPD (CoherentParentDependency) ensures happens correctly.

Removing the CPD ensures that the runtimeconfig.json embedded in the WindowsDesktop shared runtime points to the same runtime (Microsoft.NetCore.App) that is bundled with the SDK.

In an ideal world, WinForms and WPF would build against the version of Microsoft.NetCore.App that will be eventually bundled into the SDK - and thus the CPD would continue to be retained in dotnet/windowsdesktop repo. Today, we are unable to ingest newer versions of Microsoft.NetCore.App due to tooling problems (see links/discussion below), so this workaround is being added.

Related:

• [master] Update dependencies from dotnet/winforms wpf#2118
• Revert versions to f3ac1266 level, where MicrosoftNETCoreApppackageVersion=5.0.0-alpha1.19514.1 winforms#2497
• Merge pull request #2707 from RussKie/Unblock_flow_to_WindowsDesktop winforms#2707

/cc @dotnet/wpf-developers, @mmitche, @wtgodbe, @RussKie , @AdamYoblick, @nguerrera, @dsplaisted, @ericstj, @tgani-msft, @jeffschwMSFT

[vatsan-madhavan]

/azp run

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