Remove WindowsDesktop from Core-Setup, now dotnet/windowsdesktop

[dagood]

This shared framework will now be produced from dotnet/windowsdesktop instead of this repo. https://github.com/dotnet/core-setup/issues/5732.

The removed files here were already copied over by dotnet/windowsdesktop#1.

I have an example Core-SDK PR to change where it gets the WD sharedfx from from over at dotnet/installer#5161.

[MichaelSimons]

I did a quick search on WindowsDesktop across the repo. There are a few references that I'm curious if they are still needed. For the most part they seem benign but would make sense to cleanup.

1. https://github.com/dotnet/core-setup/blob/6f12a57e3c1a5e0bc592745b2648b041819ae4ed/src/test/Microsoft.DotNet.CoreSetup.Packaging.Tests/WindowsDesktopTests.cs

2. core-setup/src/pkg/packaging-tools/framework.dependency.targets

   Line 340 in b903a6e

   <!-- The following is necessary to crossgen WindowsDesktop. For NETCoreApp it's automatic because we're crossgenning CoreFX bits. -->

   
   etc...

[dagood]

https://github.com/dotnet/core-setup/blob/6f12a57e3c1a5e0bc592745b2648b041819ae4ed/src/test/Microsoft.DotNet.CoreSetup.Packaging.Tests/WindowsDesktopTests.cs

Already deleted this with the second commit. 😄 4178fd8 Leaving this in actually causes a failure, as it should.

core-setup/src/pkg/packaging-tools/framework.dependency.targets

This file will be deleted when I switch Core-Setup to the tooling package, no need to clean up refs in that dir. https://github.com/dotnet/core-setup/issues/4787