unexport spec checking helpers

[simonpcouch]

After working through integrating these new helpers in tidymodels, it looks like we don't actually need to use them outside of parsnip. A note from the last planned PR to integrate them, adding a failure on add_model in workflows:

The thought is that we fail early enough to prevent people from running computationally intensive things before running into issues [with missing extensions]. In practice, I think parsnip makes this happen most of the time: if a user is tuning a workflow and that workflow uses an engine that isn't loaded, then all models will fail with the parsnip error and that tuning will only take a second or two.

It is true that if a user is tuning a workflowset, and some needed extensions are loaded while others are not, the specs with loaded extensions will tune fully before notifying the user that the others failed...

[github-actions]

This pull request has been automatically locked. If you believe you have found a related problem, please file a new issue (with a reprex: https://reprex.tidyverse.org) and link to this issue.