[DRE-maint] open-build-service is marked for autoremoval from testing

[Debian testing autoremoval watch]

open-build-service 2.7.1-9 is marked for autoremoval from testing on 2017-02-01

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