Remove url options

Removing url options because It does not works at all.
Thus, there are others PR at the moment to include url(links) as well.

test/fixtures/active_record.rb

@@ -40,7 +40,6 @@ module ARModels
 
     has_many :comments
     belongs_to :author
-    url :comments
   end
 
   class CommentSerializer < ActiveModel::Serializer

test/fixtures/poro.rb

@@ -59,8 +59,6 @@ end
 class ProfileSerializer < ActiveModel::Serializer
   attributes :name, :description
 
-  urls :posts, :comments
-
   def arguments_passed_in?
     options[:my_options] == :accessible
   end
@@ -68,8 +66,6 @@ end
 
 class ProfilePreviewSerializer < ActiveModel::Serializer
   attributes :name
-
-  urls :posts, :comments
 end
 
 Post     = Class.new(Model)
@@ -100,7 +96,6 @@ PostSerializer = Class.new(ActiveModel::Serializer) do
   has_many :comments
   belongs_to :blog
   belongs_to :author
-  url :comments
 
   def blog
     Blog.new(id: 999, name: 'Custom blog')

test/serializers/urls_test.rb

@@ -1,25 +0,0 @@
-require 'test_helper'
-
-module ActiveModel
-  class Serializer
-    class UrlsTest < Minitest::Test
-      def setup
-        @profile = Profile.new({ name: 'Name 1', description: 'Description 1', comments: 'Comments 1' })
-        @post = Post.new({ title: 'New Post', body: 'Body' })
-        @comment = Comment.new({ id: 1, body: 'ZOMG A COMMENT' })
-        @post.comments = [@comment]
-
-        @profile_serializer = ProfileSerializer.new(@profile)
-        @post_serializer = PostSerializer.new(@post)
-      end
-
-      def test_urls_definition
-        assert_equal([:posts, :comments], @profile_serializer.class._urls)
-      end
-
-      def test_url_definition
-        assert_equal([:comments], @post_serializer.class._urls)
-      end
-    end
-  end
-end