Author: Tim Hunt
MDL-63260 qtype_random: orphaned random questions should be deleted
This fix is based on some original code written by Bo Pierce.
http://git.moodle.org/gw?p=moodle.git;a=commit;h=2fbd8e9ec0dd0662f076feb48150fb9a3f8bd153
http://github.com/moodle/moodle/commit/2fbd8e9ec0dd0662f076feb48150fb9a3f8bd153
+ 3.7 en [taskunusedrandomscleanup,qtype_random]