Revert "[C10] PG observability hooks. (#108815)"
This reverts commit 0c7a877745f98b8fce8868291408945c0dd817d6.
Reverted https://github.com/pytorch/pytorch/pull/108815 on behalf of https://github.com/albanD due to Add a new torch.distributed.hooks namespace but does not document it, test was added this morning ([comment](https://github.com/pytorch/pytorch/pull/108815#issuecomment-1751327751))
