Revert D20781624: Add NCCL Alltoall to PT NCCL process group
Test Plan: revert-hammer
Differential Revision:
D20781624 (https://github.com/pytorch/pytorch/commit/b87f0e5085d30e1a1849436e6b9065edbe94e43d)
Original commit changeset: 109436583ff6
fbshipit-source-id: 03f6ee4d56baea93a1cf795d26dd92b7d6d1df28
