Revert "Move tensor grouping to ATen (#100007)"
This reverts commit 74b7a6c75e698378882d30958908073407f97fb3.
Reverted https://github.com/pytorch/pytorch/pull/100007 on behalf of https://github.com/izaitsevfb due to Breaks internal builds, see D46629727 ([comment](https://github.com/pytorch/pytorch/pull/100007#issuecomment-1587861598))
