Deleting migrated content requires all fields filled out

Problem

If you click `delete` on a documentation page it will fail (with helpful error message) if any of the required fields are not filled in.

Steps to reproduce:

• create documentation page (haven't confirmed a new one will work - only done by migrating old content)
• edit documentation page
• click `delete` with no value under summary. Complains that value is required. But it shouldn't be required for deleting the page.

Proposed resolution:

- maybe autofill the summary with the first xx chars from the body when migrating instead of leaving the required field empty?
- or prevent some form checking when deleting?