Remove tools/setup_helpers/nvtoolext.py (do not seem to be used) (#28125)
Summary:
`git grep nvtoolext` shows nothing (meaning that it is never imported).
Pull Request resolved: https://github.com/pytorch/pytorch/pull/28125
Differential Revision: D17979164
Pulled By: ezyang
fbshipit-source-id: 7cfe770c9f7140c8ad58676f912037e6226647d3
