Revert "[PyTorch] Use c10::FastMap for memoizing in Pickler (#96360)" (#96547)
This reverts commit 69d3fa2e4d93f3367ceb3af62d78aedd317dca6c.
Reason: breaks internal meta tests. See [D43926671](https://www.internalfb.com/diff/D43926671)
Pull Request resolved: https://github.com/pytorch/pytorch/pull/96547
Approved by: https://github.com/seemethere, https://github.com/malfet
