Fix flag admin url resolving
The url resolving for the flag admin still belived we had different post admins for
each area. This is no longer the case.
Also adding a test, that checks for this issue.
Side note: I also saw some debug output, the test admin still head. Removed that.
- Flag a post and check flag admin.
- Click on link to post admin
Reviewed By: WyldBot
Differential Revision: https://phabricator.wildfyre.net/D240