[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 2018-03-08

It (build-)depends on packages with these RC bugs:
887306: obs-build: CVE-2017-14804: Exploit extractbuild to write to files in the host system
888121: ruby-delayed-job-active-record: FTBFS on ruby2.5: `method_missing': undefined method `yaml_as'
888189: ruby-innertube: FTBFS on ruby2.5: undefined method mock
888193: ruby-rmagick: FTBFS on ruby2.5: <FrozenError(<can't modify frozen Magick::Image>)>
888196: ruby-sexp-processor: FTBFS on ruby2.5: BOOM GOES THE STACK
890699: ruby-rspec-rails: FTBFS and Debci failure with ruby-rspec 3.7.0c1e0m0s1-1