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/aliases.erb

@@ -1,10 +0,0 @@
-#
-# Auto-generated by Chef.
-# Local modifications will be overwritten.
-#
-# See man 5 aliases for format
-postmaster:    root
-
-<% node['postfix']['aliases'].each do |name, value| %>
-<%= name %>: <%= [value].flatten.map{|x| if (x.include?("@")) then x else %Q("#{x}") end}.join(', ') %>
-<% end unless node['postfix']['aliases'].nil? %>