Remove three cpu sigmoid functions that are identical to IMPLEMENT_UNARY_OP_VEC (#22271)
Summary:
This does not occur in CUDA code.
Pull Request resolved: https://github.com/pytorch/pytorch/pull/22271
Differential Revision: D16024605
Pulled By: bddppq
fbshipit-source-id: bb4f16bacbdc040faa59751fba97958f4c2d33cd
