Do not vendor cookbooks using Berkshelf anymore

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

cookbooks/composer/recipes/self_update.rb

@@ -1,16 +0,0 @@
-#
-# Cookbook Name:: composer
-# Recipe:: self_update
-#
-# Copyright (c) 2016, David Joos
-#
-
-include_recipe 'composer::install'
-
-execute 'composer-self_update' do
-  cwd node['composer']['install_dir']
-  command 'composer self-update'
-  environment 'COMPOSER_HOME' => Composer.home_dir(node)
-  action :run
-  ignore_failure true
-end