Revert "[c10d] PGNCCL refactor part 1: adds assert size==1 (#119099)"
This reverts commit 4ab852b6c558a0b8e9fea0c863c782fe65f00be0.
Reverted https://github.com/pytorch/pytorch/pull/119099 on behalf of https://github.com/atalman due to Breaks internal tests ([comment](https://github.com/pytorch/pytorch/pull/119099#issuecomment-1930839754))
