Drop unused column

Summary: https://secure.phabricator.com/D1830?id=3203#inline-2058

Test Plan:
Run script on db containing this column.
Run script on db not containing this column.
Visit /repository/.

Reviewers: epriestley

Reviewed By: epriestley

CC: aran, epriestley

Differential Revision: https://secure.phabricator.com/D1854