Revert D26009829: Optimize relu on cpu using clamp_min
Test Plan: revert-hammer
Differential Revision:
D26009829 (https://github.com/pytorch/pytorch/commit/2054cd56c53f4ae2d5e3086e9ae26e89b8df531f)
Original commit changeset: 7bb1583ffb3e
fbshipit-source-id: 3e945b438fb8d83f721e400ae69be8848cab9720
