Remove Overridden Question Attributes in Documentation

What is the purpose of this pull request?

[x] Documentation update
[ ] Bug fix
[ ] Feature addition or enhancement
[ ] Code maintenance
[ ] DevOps
[ ] Improve developer experience
[ ] Others, please explain:

Fixes #2512 Related to #2511

Overview of changes:

Remove header and hint attributes in question with header and hint slots.

Anything you'd like to highlight/discuss:

The page on the User Guide in question is this. Expand the panel entitled Header and Hint example with slots.

This still achieves the purpose of the documentation, which is to show how slots can replace the header and hint attributes.

Testing instructions:

Switch to the branch for PR #2511, navigate to the docs directory and run markbind serve -d. Logger warnings should appear. Then, make the changes in this PR, and run markbind serve-d again. There should not be logger warnings anymore.

Proposed commit message: (wrap lines at 72 characters)

Remove Overridden Question Attributes in Docs

The docs currently has a question where there are slots overriding
the header attributes. However, when #2511 is merged, logger
warnings about this overriding will be triggered, leading to the
check-docs GitHub action failing.

Let's remove the header attributes so that they will not trigger
the logger warning. Let's also update the sample code to reflect
this change.

Checklist: :ballot_box_with_check:

[x] Updated the documentation for feature additions and enhancements
[ ] Added tests for bug fixes or features
[x] Linked all related issues
[x] No unrelated changes

Reviewer checklist:

Indicate the SEMVER impact of the PR:

[ ] Major (when you make incompatible API changes)
[ ] Minor (when you add functionality in a backward compatible manner)
[x] Patch (when you make backward compatible bug fixes)

At the end of the review, please label the PR with the appropriate label: r.Major, r.Minor, r.Patch.

Breaking change release note preparation (if applicable):

To be included in the release note for any feature that is made obsolete/breaking

Give a brief explanation note about:

what was the old feature that was made obsolete

any replacement feature (if any), and

how the author should modify his website to migrate from the old feature to the replacement feature (if possible).

MarkBind / markbind

Remove Overridden Question Attributes in Documentation #2513