Further reduce windows build/test matrix (#40592)
Summary:
Switch windows CPU testers from `windows.xlarge` to `windows.medium` class.
Remove VS 14.16 CUDA build
Only do smoke force-on-cpu tests using VS2019+CUDA10.1 config.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/40592
Differential Revision: D22259351
Pulled By: malfet
fbshipit-source-id: f934ff774dfc7d47f12c3da836ca314c12d92208
