Remove deployment configuration for neon.ruby-lang.org

I finished to prepare heroku environment. I decided to migrate neon.ruby-lang.org to www-ruby-lang.herokuapp.com.

We need to finish following tasks:

 - [x] Add deploy grant of www-ruby-lang.herokuapp.com to editorial team. Please notice your mail address of heroku account to me.
 - [x] Confirmation of deployment used heroku on editorial team.
 - [x] Apply CNAME of www.ruby-lang.org to www-ruby-lang.herokuapp.com (and staging)
 - [x] Merge this pull request
 
@ruby/www.ruby-lang.org How do you think about this?

/cc @hone @ayumin