Back out "Revert D25717510: Clean up some type annotations in benchmarks/fastrnns" (#50556)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/50556
Original commit changeset: 2bcc19cd4340
Test Plan: Soft revert hammer
Reviewed By: walterddr, seemethere
Differential Revision: D25917129
fbshipit-source-id: e5caad77655789d607b84eee820aa7c960e00f51
