When viewing guestbook responses, there's always a Custom Questions column even when the guestbook never included custom questions

What steps does it take to reproduce the issue?

• Create a Dataverse Collection
• Create a guestbook in that collection that has no custom questions
• Visit the collection's Manage Guestbooks page
• Click View Responses for the guestbook you created and see that there's a column for custom questions
• Create a dataset in that collection
• Add a file to the dataset
• Add the guestbook to that dataset
• Publish the dataset
• Download the file in the dataset
• Visit the collection's Manage Guestbooks page again
• Click View Responses for the guestbook you created and see that for the response that your download created, there's a column for custom questions
• Go back to the Manage Guestbook page and click Download Responses
• See that the CSV file includes a column for custom questions

When does this issue occur?
When viewing the responses of a guestbook that has never included custom questions

Which page(s) does it occurs on?
On the Manage Guestbook page and in the CSV file users get when they download the guestbook

What happens?
The table on the page and in the CSV file includes a "Custom Questions" column, even when guestbook has never had a custom questions

To whom does it occur (all users, curators, superusers)?
Curators, Dataverse Collection owners

What did you expect to happen?
The "Custom Question" column appears only when the guestbook has or has had one or more custom questions

Which version of Dataverse are you using?
v5.9

Any related open or closed issues to this bug report?
https://github.com/IQSS/dataverse/issues/1730 (particularly this comment)

Screenshots:

Start by reproducing the issue from the Manage Guestbooks page: open View Responses for a guestbook without custom questions, then check Download Responses and the resulting CSV. Trace the response table and CSV entry points to determine why the Custom Questions column is included. Done means both views omit that column unless the guestbook has or had custom questions.