[PyTorch][Edge] Fix inefficiency in objLoaderMobile (#65710)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/65710
No need to incur extra refcount bumps, and no need to use a stringstream for what are presumably string keys anyway.
ghstack-source-id: 139325445
Test Plan: CI, reviewers to confirm the keys are supposed to be strings
Reviewed By: dhruvbird
Differential Revision: D31215347
fbshipit-source-id: 82be93cb2e57aefe94edf74d149115cb734112be
