Remove old position-on-read board column code

Summary: Ref T10010. This retires the old way of doing things inside ColumnPositionQuery. It is now obsolete and lives in BoardLayoutEngine instead.

Test Plan:

• Moved cards, created cards, swapped filters, orders, etc.
• Some degree of unit testing coming in the next diff.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T10010

Differential Revision: https://secure.phabricator.com/D15177