3237 Simpler flash message for draft chapters

https://code.google.com/p/otwarchive/issues/detail?id=3237#c22

Message on draft chapters on posted works: "This is a draft chapter in a posted work. It will be kept unless the work is deleted."

Message on draft chapters on unposted works: "This is a draft chapter in an unposted work. The work will be **automatically deleted** on Tue 22 Apr 2014 01:34AM EDT ."