Cleanup functional.py after lu_unpack was removed (#58669)
Summary:
Remove code in functional.py that became unused after PR https://github.com/pytorch/pytorch/commit/c790fd2bf89f16de25e5918e67b3e5fb6288c4cb
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58669
Reviewed By: driazati
Differential Revision: D28572377
Pulled By: heitorschueroff
fbshipit-source-id: c90d80ead5f3d69100667488bc6b14ef54b95b54
