Remove 'rails' command

It should not be run using `bundle exec`:

* http://blog.wyeworks.com/2011/12/27/bundle-exec-rails-executes-bundler-setup-3-times
* http://yehudakatz.com/2011/05/30/gem-versioning-and-bundler-doing-it-right/

bundler-exec.sh

@@ -47,7 +47,6 @@ heroku
 html2haml
 jasmine
 rackup
-rails
 rake
 rake2thor
 rspec