Check all code TODOs have been done

This final one is no longer necessary - the content has now changed to specify 'Optional', so the field is not required.

There are no other TODOs in the SSP code.

Addresses this card: https://www.agileplannerapp.com/boards/187120/cards/7900
Merge pull request #157 from alphagov/all_the_todos

Check all code TODOs have been done