[DRE-maint] Bug#1050580: ruby-roxml: broken by ruby-nokogiri 1.15.4

[Lucas Kanashiro]

Upstream is not active for some years (last commit from more than 2 
years ago), I do not expect them to fix this. I was checking the reverse 
dependencies and it seems there isn't any, I believe we should remove 
this package also from unstable (it was already removed from testing).

-- 
Lucas Kanashiro