Revert to use NCCL 2.7.8-1 (#47638)
Summary:
Only depend on stable NCCL releases
Pull Request resolved: https://github.com/pytorch/pytorch/pull/47638
Reviewed By: mingzhe09088
Differential Revision: D24847765
Pulled By: mrshenli
fbshipit-source-id: 2c5f29602aa7403c110797cb07f8fb6151a1b60d
