Remove unused PORO#to_param

Author: bf4

test/fixtures/poro.rb

@@ -33,10 +33,6 @@ def id
     @attributes[:id] || @attributes['id'] || object_id
   end
 
-  def to_param
-    id
-  end
-
   def method_missing(meth, *args)
     if meth.to_s =~ /^(.*)=$/
       @attributes[$1.to_sym] = args[0]