Revert D32704467: [Autograd/Checkpoint] Checkpoint implementation without reentrant autograd
Test Plan: revert-hammer
Differential Revision:
D32704467 (https://github.com/pytorch/pytorch/commit/e032dae32904c6e90353e90051785514d6c5a7d9)
Original commit changeset: 6eea1cce6b93
fbshipit-source-id: 1a788c1fd57cee46bba82e216e6162d078359cc2
