Completely Remove FutureMessage from RPC cpp tests (#50027)
Summary: Pull Request resolved: https://github.com/pytorch/pytorch/pull/50027
Test Plan: Imported from OSS
Reviewed By: lw
Differential Revision: D25753815
Pulled By: mrshenli
fbshipit-source-id: 85b9b03fec52b4175288ac3a401285607744b451
