remove c10_defs.bzl and embed its logic directly where it is used (#84595)
Differential Revision: [D39287079](https://our.internmc.facebook.com/intern/diff/D39287079/)
**NOTE FOR REVIEWERS**: This PR has internal Facebook specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D39287079/)!
Pull Request resolved: https://github.com/pytorch/pytorch/pull/84595
Approved by: https://github.com/DanilBaibak
Author
Michael Andreas Dagitses