Revert D22208758: [pytorch][PR] Report error when ATEN_THEADING is OMP and USE_OPENMP is turned off.
Test Plan: revert-hammer
Differential Revision:
D22208758 (https://github.com/pytorch/pytorch/commit/3ed96e465cbbb8c7f9ea4fea2abe3cb84dac535d)
Original commit changeset: 0866c9bb9b3b
fbshipit-source-id: 9e2b469469e274292b2559c02aa0256425fd355e
