Revert D25399468: optimize channels last for BatchNorm2d on CPU
Test Plan: revert-hammer
Differential Revision:
D25399468 (https://github.com/pytorch/pytorch/commit/0be334a1baba4a96a1341e8951e25a03bcf71301)
Original commit changeset: a4cd7a09cd4e
fbshipit-source-id: cef74881adcdf193355fa5a77e816addd2e2c56e
