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 
It does, because the behavior is different for inline and tabbed discussions. In particular, the code has to press the "Show Discussion" button for inline discussions.