[DRE-maint] ohai is marked for autoremoval from testing

[Debian testing autoremoval watch]

ohai 8.21.0-1 is marked for autoremoval from testing on 2018-04-19

It is affected by these RC bugs:
892196: ohai: ohai FTBFS with Ruby 2.5

It (build-)depends on packages with these RC bugs:
892186: chef: FTBFS and Debci failure with Ruby 2.5