No-op the old repository credential migration

Summary:
Ref T8746. See discussion there. We could try harder to fix this but I suspect the number of affected installs is exceedingly small since it's ~18 months old. Requiring reconfiguration of credentials seems reasonable-ish.

Also fix a merge issue with Conpherence search.

Test Plan: N/A

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Maniphest Tasks: T8746

Differential Revision: https://secure.phabricator.com/D13565