Clean up old feature settings code

[JakePT]

Is your enhancement related to a problem? Please describe.

The new features screen uses settings_schema and the get_json method of the Feature class. Code for the old settings page should probably be removed and/or deprecated. This includes:

• Feature::output_feature_box_summary
• Feature::output_feature_box_long
• Feature::output_feature_box
• Feature::output_feature_box_settings
• Feature::output_settings_box
• Feature::get_epio_logo
• Features::update_feature
• Anything hooked to ep_sanitize_feature_settings
• assets/js/instant-results/admin
• Anything in assets/js/dashboard.js related to feature settings.

Designs

No response

Describe alternatives you've considered

No response

Code of Conduct

• I agree to follow this project's Code of Conduct