Remove the repositories application

Summary: Fixes T7603. This application is no longer used.

Test Plan: Went to /repository/ and got a 404.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: epriestley

Maniphest Tasks: T7603

Differential Revision: https://secure.phabricator.com/D12734