'View only' custom fields leave empty <dt> row on forms

If a "view only" field is created as part of a custom data group, then the field does not show up in its 'Edit' view., but it does leave a ghost trail:

<dt/>
<dd class="html-adjust"/>

The extra <dt> elements adds extra space between the other elements which disrupts the spacing.

To recreate:
1. Create a custom data group that applies to Contacts
2. Add text fields. Make one of them in the middle 'View only' = TRUE
3. View the Edit page for a Contact, and see the extra space where the hidden field might have been

e.g. on the current dev server edit a contact and look at the "Contact Extras" group