[FX] Fix issue where GraphModule.delete_all_unused_submodules deletes submodules from called leaf modules (#66430)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/66430
On the whole, I'm not totally satisfied with this approach. I think we should be building a prefix tree data structure during initial iteration over the submodules and querying that when deleting submodules. But I think this approach works and I want to see if we can get it in before 1.10
Test Plan: Imported from OSS
Reviewed By: Chillee
Differential Revision: D31546137
Pulled By: jamesr66a
fbshipit-source-id: f08b8409a3cf511277017ccccb916097b7c4c4fe
