[docs] `rule_overridable` incorrectly included in quizaccess plugin type documentation.

[marxjohnson]

What is the URL of the page?

https://moodledev.io/docs/5.0/apis/plugintypes/quizaccess

What is the issue with this page?

This documentation was merged prematurely before the tracker issue that introduced rule_overridable was complete. This has caused some confusion. The API has been refactored during review, meaning the documented version will never be correct. It should be removed, then replaced with a corrected version when MDL-80945 is complete.

Are you able to provide a patch for this?

Yes - I will create one