Remove subgraphNode kind assert in unmergeSubgraph (#31212)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/31212
To be able to use this function more broadly.
Test Plan: unit tests
Reviewed By: jackm321
Differential Revision: D18978913
fbshipit-source-id: d998dc7c7f9540f491a8a4bc5d6d25d9c3bf8764
