Declaration:status problem

This is presumably a beta-blocker, so I'll comment on it to bump it up the list.

I suggest we remove all code related to declaration status for now. I'm not clear enough what problem this is trying to solve, to know what constraints the solution needs to obey.

The code we can remove is:
Declaration::statusOptions()
Declaration status field
DeclarationInterface status constants
Drupal\gift_aid\Plugin\Field\DeclarationStatusItemList