Remove PhabricatorOwnersOwner::loadAffiliatedPackages()

Summary: See D3193 for discussion.

Test Plan: Ran owners.query via conduit, verified I got sensible output.

Reviewers: vrana, btrahan, meitros

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T603

Differential Revision: https://secure.phabricator.com/D3194