[DDP] Remove train call to module copies (#58595)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58595
No longer needed since this list is always of size 1.
ghstack-source-id: 129498229
Test Plan: CI
Reviewed By: zhaojuanmao
Differential Revision: D28548426
fbshipit-source-id: 7d6dba92fff685ec7f52ba7a3d350e36405e2578
