Bug 24865: (QA follow-up) Remove hardcoded notice name from protected_letters

Bug 24865: (QA follow-up) Remove hardcoded notice name from protected_letters

If the letter has been removed, fall back to itemnumber/due date. (Title is
no longer fetched.) We may assume that the notice is present.

Note: The option to 'protect' a notice may need some more thought. Perhaps
it needs to be an attribute on itself.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Tested by deleting notice, running fines again.
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>