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/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