pytorch

4503c455 - Remove registration of NNC backend. (#81160)

Remove registration of NNC backend. (#81160) It looks like we sometimes try to register the backend more than once. Since it's not actually used now, let's simply disable it. @bypass-github-export-checks Differential Revision: [D37734986](https://our.internmc.facebook.com/intern/diff/D37734986/) **NOTE FOR REVIEWERS**: This PR has internal Facebook specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D37734986/)! Differential Revision: [D37734986](https://our.internmc.facebook.com/intern/diff/D37734986) Pull Request resolved: https://github.com/pytorch/pytorch/pull/81160 Approved by: https://github.com/suo