[caffe2] Don't copy Tensor dims during deserialization (#79471)
We can just make an IntArrayRef.
Differential Revision: [D37124427](https://our.internmc.facebook.com/intern/diff/D37124427/)
**NOTE FOR REVIEWERS**: This PR has internal Facebook specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D37124427/)!
Pull Request resolved: https://github.com/pytorch/pytorch/pull/79471
Approved by: https://github.com/ezyang
