temporarily disbale layernorm AD (#20442)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20442
ghimport-source-id: c246ade4ee9ee31b2e3413efff3ea6a246e1837e
Differential Revision: D15321524
Pulled By: wanchaol
fbshipit-source-id: 22c77d08c91af2d83dfd2c4a84cafc56e9240033
