[DDP] Don't find tensors if static graph (#58105)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/58105
When find_unused_parameters=True but static_graph is also set, static graph handles unused parameter accounting, so this code path is not needed
ghstack-source-id: 128736289
Test Plan: CI
Reviewed By: zhaojuanmao
Differential Revision: D28371954
fbshipit-source-id: 0b42a9c0fd2bba26a0de288436e9c7139e292578
