Revert D30745921: [DDP] Fix when buffers are reassigned in module
Test Plan: revert-hammer
Differential Revision:
D30745921 (https://github.com/pytorch/pytorch/commit/d59ecc02df70bad2273858c2fad2b4993133a3d3)
Original commit changeset: 25eb1edbf445
fbshipit-source-id: 343ead86bf1e2d0b2d4124be331ea2fa437303ad
