Revert D31732415: Add support for cat in output stitching
Test Plan: revert-hammer
Differential Revision:
D31732415 (https://github.com/pytorch/pytorch/commit/b4db5174fe17a53745e47e2e5dcbee2ba3ad5b65)
Original commit changeset: 7f513cea355f
fbshipit-source-id: a0d8f1512b13d51f6e50b5da58084effbaf0a0dc
