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

[Debian testing autoremoval watch]

open-build-service 2.7.4-2 is marked for autoremoval from testing on 2018-04-16

It (build-)depends on packages with these RC bugs:
888189: ruby-innertube: FTBFS on ruby2.5: undefined method mock
892189: ruby-mini-magick: FTBFS and Debci failure with imagemagick 8:6.9.9.34+dfsg-3
892457: ruby-jquery-ui-rails: ruby-jquery-ui-rails FTBFS with Ruby 2.5
892507: ruby-sequel: ruby-sequel FTBFS with Ruby 2.5