Do not vendor cookbooks using Berkshelf anymore

Instead, use the Berkshelf support in knife-solo and the
vagrant-berkshelf plugin on Vagrant

cookbooks/hostname/Gemfile

@@ -1,13 +0,0 @@
-source 'https://rubygems.org'
-
-gem 'berkshelf'
-gem 'chef', '~> 12.13'
-gem 'chefspec'
-gem 'foodcritic'
-gem 'rake'
-gem 'rubocop'
-
-group :integration do
-  gem 'kitchen-vagrant'
-  gem 'test-kitchen'
-end