Remove out of supported choice

[Varorbc]

test-templates/template_feed/Microsoft.DotNet.Test.ProjectTemplates.9.0/content/MSTest-CSharp/.template.config/template.json

Line 64 in f6920c3

"choice": "netcoreapp3.1",

[Evangelink]

Hi @Varorbc,

We are aware this is deprecated but we still have many big customers relying on deprecated TFMs. We are currently starting discussions with all parties to understand when we can remove the deprecated options.

[Varorbc]

I think we could take a look at the ASP.NET Core project templates for reference. They've got templates for different versions, but inside each template, there's only the latest version available.

[Evangelink]

This was the default for MSTest before .NET 9 and it is still the default for xUnit and NUnit templates. We had many complaints from users that couldn't understand why the versions were always out of date and why the templates were different when selecting different TFM.

There are some fundamental difference in expectations from users when working with tests or production code.