Exporting individual form with XLSX on an issue exports hidden fields as blank

Issue Summary

Exporting a single form on an issue with XLSX will still export the columns for fields which are hidden by conditional sections as blank fields.

Steps to Reproduce

1. Go to an issue
2. Select a form
3. Select Download XLSX

This can also be reproduced with the Get XLSX endpoint in Public API.

Expected Results

Only visible fields are exported as columns.

Actual Results

All fields on the form are exported as columns, including those hidden by conditional sections. They will be blank.

Workaround

Filter out the columns manually from the XLSX file.