CLC-4276 - Expire cache on /api/my/status when opting in / out of the calendar option

https://jira.ets.berkeley.edu/jira/browse/CLC-4276
This method is highly likely to get mixed up with self.expire, defined above. 

Could you please relocate the new expire method to ApplicationController and call it something like expire_current_user? And then use the current_user method to get the user instead of going directly to session[:user_id].