Remove RValue env

Pull Request resolved: #1992

StreamWorker now directly stores a python environment rather than RValue. Now IValue/RValue are almost entirely unused within the workers, and WireValue is only used to interface with some tests. Follow ups will  re-implement Tenosor/TensorCell as a wrapper around a python torch tensor. Then we can begin to remove torch-sys's libtorch bindings.
ghstack-source-id: 325670318
@exported-using-ghexport

Differential Revision: [D87835914](https://our.internmc.facebook.com/intern/diff/D87835914/)

**NOTE FOR REVIEWERS**: This PR has internal Meta-specific changes or comments, please review them on [Phabricator](https://our.internmc.facebook.com/intern/diff/D87835914/)!

Author: zdevito