Removes pickle deprecation warning (#39003)
Summary:
As per [this issue](https://github.com/pytorch/pytorch/issues/38597), this is a one-line PR to remove the pickle deprecation warning.
cc stsievert driazati
Pull Request resolved: https://github.com/pytorch/pytorch/pull/39003
Differential Revision: D21723048
Pulled By: ezyang
fbshipit-source-id: f6cc8f28b8140edd7b46d1f26f2d99819beb933e
