R1:ca182c7f48ca

Clean up "Audit Authority" code, at least mostly

Summary:
Ref T2393. We had three copies of this code ("which packages/projects can a user accept on behalf of?"). I removed one in D17250. This consolidates the other two.

This still isn't perfect and it should probably live in a Query or something some day, but there's some weird stuff going on with the viewer in the editor context, and at least the code handles the viewer correctly now and isn't living somewhere weird and totally unrelated to auditing…