Revert D23236088: [pytorch][PR] [caffe2] adds Cancel to SafeDequeueBlobsOp and SafeEnqueueBlobsOp
Test Plan: revert-hammer
Differential Revision:
D23236088 (https://github.com/pytorch/pytorch/commit/0ccc38b77390f34bb173885ff039363d2931c356)
Original commit changeset: daa90d9ee324
fbshipit-source-id: 933c7deab177250075683a9bea143ac37f16a598
