Remove TH/THC link for single matrix inverse (#20534)
Summary:
- Earlier, we had to use the legacy implementation of `getri` for single matrix inverse from TH and THC
- Now, this has been moved to ATen
Changelog:
- Move single matrix inverse implementation to ATen
- Remove unused code in TH and THC resulting from the change
- Minor modifications made to single matrix CPU function implementations in ATen to avoid redundancy
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20534
Differential Revision: D15393383
Pulled By: ezyang
fbshipit-source-id: 81972111cd9757d15f1d634f294c93fd0f35636c
