Restore class method from_json, as event is no more an included class

lib/logstash/event.rb

@@ -57,18 +57,10 @@ def initialize(data={})
     data["@version"] = "1" if !@data.include?("@version")
   end # def initialize
 
-  # Add class methods on inclusion.
   public
-  def self.included(klass)
-    klass.extend(ClassMethods)
-  end # def included
-
-  module ClassMethods
-    public
-    def from_json(json)
-      return self.new(JSON.parse(json))
-    end # def from_json
-  end
+  def self.from_json(json)
+    return self.new(JSON.parse(json))
+  end # def from_json
 
   public
   def cancel