Delete tools/autograd/env.py (#25920)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/25920
It's not necessary anymore
Test Plan
- [namedtensor ci]
Test Plan: Imported from OSS
Differential Revision: D17285053
Pulled By: zou3519
fbshipit-source-id: 56dc18d1d49a0df7dacda880189e6c2fb09bc5f6
