pytorch

4aa30d3c - Revert D18293522: Optimize LayerNorm with explicit vectorization using Vec256

Revert D18293522: Optimize LayerNorm with explicit vectorization using Vec256 Test Plan: revert-hammer Differential Revision: D18293522 Original commit changeset: f4cfed6e62ba fbshipit-source-id: cdd6d9d36c00b516aecdab549abeeffc4a473829