Simplify extending Formula with Enumerable

Library/Homebrew/formula.rb

@@ -14,6 +14,7 @@ require 'pkg_version'
 class Formula
   include FileUtils
   include Utils::Inreplace
+  extend Enumerable
 
   attr_reader :name, :path, :homepage, :build
   attr_reader :stable, :devel, :head, :active_spec
@@ -358,9 +359,6 @@ class Formula
       end
     end
   end
-  class << self
-    include Enumerable
-  end
 
   # An array of all installed formulae
   def self.installed