Don't show cohort information when disabled

TNL-552

@cahrens and I decided that it would be cleaner to have the server return responses as if cohorting had never been enabled, rather than to teach the front end how to ignore the cohort fields.

Reviewers: @cahrens @jimabramson 
Errr, because I didn't know that existed. :-) I did a search around and other code that I saw seemed to be doing it this way. I'll switch it.