Revert D32286934: [pytorch][PR] replace platform specific CI environment variables with generic ones
Test Plan: revert-hammer
Differential Revision:
D32286934 (https://github.com/pytorch/pytorch/commit/7d931fb082fb02af83db0fe0e530ae779580fb7c)
Original commit changeset: 1008938088da
fbshipit-source-id: dd2dd07742670a34deec10995b95b98c9fd62724
