Clean up remaining default column logic for boards
Summary: See D10189. We should never hit this anymore, so clean it up.
Test Plan:
- Reloaded a board, saw everything stay where it was before the change.
- Added a new task to the project, saw it show up in backlog.
Reviewers: btrahan
Reviewed By: btrahan
Subscribers: epriestley
Differential Revision: https://secure.phabricator.com/D10200