Revert D28994140: [pytorch][PR] Implemented torch.cov
Test Plan: revert-hammer
Differential Revision:
D28994140 (https://github.com/pytorch/pytorch/commit/23c232554bfc138d0d082ea8ea8e8ecec51e30ae)
Original commit changeset: 1890166c0a9c
fbshipit-source-id: 73dfe1b00464e38f004f99960cdeeb604ed4b20a
