PG NCCL cleanup: remove usage of completed_ in WorkNCCL copies (#59899)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/59899
Test Plan: Imported from OSS
Reviewed By: cbalioglu, osalpekar
Differential Revision: D29080299
Pulled By: agolynski
fbshipit-source-id: 9ae368f91e81f19471e0a20fc913d8e9df1b9dec
