Replace FutureMessage with ivalue::Future in RpcAgent retry logic (#49995)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/49995
Test Plan: Imported from OSS
Reviewed By: lw
Differential Revision: D25745301
Pulled By: mrshenli
fbshipit-source-id: b5e3a7e0b377496924847d8d70d61de32e2d87f4
