[DRE-maint] ruby-riddle is marked for autoremoval from testing

[Debian testing autoremoval watch]

ruby-riddle 1.5.12-3 is marked for autoremoval from testing on 2017-02-16

It is affected by these RC bugs:
841601: ruby-riddle: FTBFS: ERROR: Test "ruby2.3" failed.
848289: ruby-riddle: (build-)depends on mysql-{client,server}