doc: Remove Ruby on Rails 6.0 pacakges.

www/ruby-rails60
textproc/ruby-actiontext60
devel/ruby-railties60
www/ruby-actioncable60
mail/ruby-actionmailbox60
devel/ruby-activestorage60
mail/ruby-actionmailer60
databases/ruby-activerecord60
www/ruby-actionpack60
www/ruby-actionview60
devel/ruby-activejob60
devel/ruby-activemodel60
devel/ruby-activesupport60

(taca)