Some essential changes needed before updating the Windows AMI (#20353)
Summary:
1. Add cuda 10.1 build
2. Turn on openmp loop support for VS 2019
3. Remove legacy code about selective builds
Tested through CI.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20353
Differential Revision: D15294806
Pulled By: ezyang
fbshipit-source-id: 0acf5c3fbbc398fd9ebdf9f97653499d39638432
