Define layer_norm schema in caffe2 (#16535)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16535
There is now no need anymore to define the layer norm schema in a central location.
It can just be defined in caffe2 next to the kernel implementation.
Reviewed By: ezyang
Differential Revision: D13869503
fbshipit-source-id: c478153f8fd712ff6d507c794500286eb3583149
