Use ivalue::Future in autograd engine and DistEngine. (#43676)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43676
This is one part of https://github.com/pytorch/pytorch/issues/41574 to
ensure we consolidate everything around ivalue::Future.
I've removed the use of torch/csrc/utils/future.h from the autograd engines and
used ivalue::Future instead.
ghstack-source-id: 110895545
Test Plan: waitforbuildbot.
Reviewed By: albanD
Differential Revision: D23362415
fbshipit-source-id: aa109b3f8acf0814d59fc5264a85a8c27ef4bdb6
