Revert D23632280: [c10d] switch ProcessGroup::Work to be managed by intrusive_ptr
Test Plan: revert-hammer
Differential Revision:
D23632280 (https://github.com/pytorch/pytorch/commit/0650a6166ff42a65b431f527d0f9a76f5be44e37)
Original commit changeset: 0a4642a8ffab
fbshipit-source-id: 2aa8ddb874fab11f773f4c08d740afcd865482e9
