Revert D28700259: [pytorch][PR] Migrate nonzero from TH to ATen (CPU)
Test Plan: revert-hammer
Differential Revision:
D28700259 (https://github.com/pytorch/pytorch/commit/95b1bc10094315f5f1e935a54d435dd33142e30a)
Original commit changeset: 9b279ca7c36d
fbshipit-source-id: 267afe63376be598d24c862e02e3b4b3ea75f77c
