Remove unnecessary UsingTasks when upgrading to Arcade 11

[ViktorHofer]

https://github.com/search?q=repo%3Adotnet%2Froslyn%20%22https%3A%2F%2Fgithub.com%2Fdotnet%2Froslyn%2Fissues%2F83095%22&type=code

Hits will come in after dotnet/dotnet#5909 is merged and flowed back.

[jjonescz]

Looks like this has been fixed in #84819.