Replace FutureMessage with c10::ivalue::Future in DistEngine. (#44239)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/44239
As part of https://github.com/pytorch/pytorch/issues/41574, use
c10::ivalue::Future everywhere in DistEngine.
ghstack-source-id: 111645070
Test Plan: waitforbuildbot
Reviewed By: mrshenli
Differential Revision: D23553507
fbshipit-source-id: 1b51ba13d1ebfa6c5c70b12028e9e96ce8ba51ff
