Revert "[export] Disable exported_program.__call__ (#119466)"
This reverts commit c26884f06345bf61e0843d13db84e76236ff6142.
Reverted https://github.com/pytorch/pytorch/pull/119466 on behalf of https://github.com/facebook-github-bot due to Diff reverted internally ([comment](https://github.com/pytorch/pytorch/pull/119466#issuecomment-1947384298))
