Revert D28240105: [pytorch][PR] Fix DistributedSampler mem usage on large datasets
Test Plan: revert-hammer
Differential Revision:
D28240105 (https://github.com/pytorch/pytorch/commit/a0ce8da26ee5d5b2842d4eacd94f6e26b610c777)
Original commit changeset: 4c6aa493d0f7
fbshipit-source-id: 8a0e17764c2f26c8316f88ad6c8772b08883ceee
