Consolidate Audit model with latest findAuditor function.

Per [71250326](https://www.pivotaltracker.com/story/show/71250326).  Found via ARTY.  Was getting script error, traced to duplicated Audit models and obsolete `findAuditors` function passing back a JS array instead of can.List, as the newer one does.  Fixed by eliminating duplication while preserving newer `findAuditors` function.

Also removed other duplicated models as indicated in comments.