Remove the now unused onboarding code

[dkotter]

Description of the Change

In #411 we added a new user onboarding experience that would guide a user through setup after they first activated the plugin.

In #771 we refactored our settings page significantly and as part of that, we removed the onboarding from ever loading in that new experience. The only ones that could access that onboarding were those that had deliberately used the classifai_use_legacy_settings_panel filter, which is now over 2 years old and will be removed soon.

This means the onboarding code has lived within ClassifAI for the last 2 years but hasn't actually been used by most users (if by any). As such, this PR removes all of that code.

How to test the Change

Not much to test here other than to ensure the normal settings experience still works as expected

Changelog Entry

Removed - New user onboarding experience that has only been accessible to those that are using the classifai_use_legacy_settings_panel filter set to true.

Credits

Props @dkotter

Checklist:

• I agree to follow this project's Code of Conduct.
• I have updated the documentation accordingly.
• I have added Critical Flows, Test Cases, and/or End-to-End Tests to cover my change.
• All new and existing tests pass.

[github-actions]

✅ WordPress Plugin Check Report

✅ Status: Passed

📊 Report

All checks passed! No errors or warnings found.

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[jeffpaul]

Did some light testing in Playground and things worked as expected.