Revert D29104397: Port `argmax` to structured kernels.
Test Plan: revert-hammer
Differential Revision:
D29104397 (https://github.com/pytorch/pytorch/commit/6f3da4f4bf0ddecdb13b006a1bb4b7ee9cf473a4)
Original commit changeset: 580355cf3b4e
fbshipit-source-id: e51fb79329066bc1a6364cfa44a8732908a684ed
