Move Set to dicts.py (#110522)
Summary:
A set is more of a dict than a list if you ask me.
This comes before the refactor where we implement sets and dicts via the
same logic.
X-link: https://github.com/pytorch/pytorch/pull/110522
Approved by: https://github.com/jansel
Reviewed By: izaitsevfb
Differential Revision: D50778786
fbshipit-source-id: fbaaa926fd2c571e3f7a1518ad9dd79994cf53f7
