Revert D26625807: [pytorch][PR] Deduplicate shared params before constructing Reducer in DDP
Test Plan: revert-hammer
Differential Revision:
D26625807 (https://github.com/pytorch/pytorch/commit/5c15a5bb46731d6fd749ab6477f87682ea701a0d)
Original commit changeset: f5f5959fef90
fbshipit-source-id: c875cc86b8fd21d9d64f934559f8e3126ed1d23d
