Revert "[export] Fix graph signature data model to list of specs. (#111017)"
This reverts commit 33b69509d3665f82bf91cee96f9beeef0d8e0b72.
Reverted https://github.com/pytorch/pytorch/pull/111017 on behalf of https://github.com/facebook-github-bot due to Diff reverted internally ([comment](https://github.com/pytorch/pytorch/pull/111017#issuecomment-1759292161))
