Do not vendor cookbooks using Berkshelf anymore

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

cookbooks/postfix/templates/default/virtual_aliases.erb

@@ -1,9 +0,0 @@
-#
-# Auto-generated by Chef.
-# Local modifications will be overwritten.
-#
-# See man 5 virtual for format
-
-<% node['postfix']['virtual_aliases'].each do |key, value| %>
-<%= key %> <%= value %>
-<% end unless node['postfix']['virtual_aliases'].nil? %>