hardshrink_cpu and hardshrink_backward_cpu refactoring with at::native::cpu_kernel
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/22459
Differential Revision: D16132625
Pulled By: pbelevich
fbshipit-source-id: d7eb1cd6ed04eba3d0c54feaca1e5ab2836211b5
