Revert D24659901: Add tests for DDP control flow models.
Test Plan: revert-hammer
Differential Revision:
D24659901 (https://github.com/pytorch/pytorch/commit/31c9d2efcd4a48146780662b2a933f1ce60ea3a1)
Original commit changeset: 17fc2b3ebba9
fbshipit-source-id: 26b0bdbe83cba54da4f363cfa7fc85c503aa05ab
