Describe the problem this feature would solve

We've moved our .NET Standard Code to now be the .NET Community Toolkit. 🎉🎉🎉

Its new home is now in this repo here.

Describe the solution

We migrated all the history over there as well, so now we just need to remove the following packages from our repo to complete the transfer:

• Microsoft.Toolkit
• Microsoft.Toolkit.Diagnostics
• Microsoft.Toolkit.HighPerformance
• Microsoft.Toolkit.Mvvm
• Microsoft.Toolkit.Mvvm.SourceGenerators

For anything that depends on Microsoft.Toolkit still we should update it to grab the CommunityToolkit.Common package from the MainLatest feed instead.

I believe we can also simplify our tests a bit potentially, right @Sergio0694?

@XAML-Knight mind taking a stab at opening a PR for this migration step removing these packages here in this repo? Thanks!