Removing references to ProcessGroupAgent in comments (#64051)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/64051
cc pietern mrshenli pritamdamania87 zhaojuanmao satgera rohan-varma gqchen aazzolini osalpekar jiayisuse agolynski SciPioneer H-Huang mrzzd cbalioglu gcramer23
Test Plan: Imported from OSS
Reviewed By: mrshenli
Differential Revision: D30587076
Pulled By: jaceyca
fbshipit-source-id: 414cb95faad0b4da0eaf2956c0668af057f93574
