Remove traces of embed option.

test/serializers/association_macros_test.rb

@@ -6,7 +6,7 @@ module ActiveModel
       AuthorSummarySerializer = Class.new
       class AssociationsTestSerializer < Serializer
         belongs_to :author, serializer: AuthorSummarySerializer
-        has_many :comments, embed: :ids
+        has_many :comments
         has_one :category
       end
 
@@ -21,7 +21,7 @@ module ActiveModel
       end
 
       def test_has_many_defines_reflection
-        has_many_reflection = HasManyReflection.new(:comments, embed: :ids)
+        has_many_reflection = HasManyReflection.new(:comments, {})
 
         assert_includes(@reflections, has_many_reflection)
       end

test/serializers/associations_test.rb

@@ -52,13 +52,13 @@ module ActiveModel
 
           case key
           when :posts
-            assert_equal({ embed: :ids }, options)
+            assert_equal({}, options)
             assert_kind_of(ActiveModel::Serializer.config.array_serializer, serializer)
           when :bio
             assert_equal({}, options)
             assert_nil serializer
           when :roles
-            assert_equal({ embed: :ids }, options)
+            assert_equal({}, options)
             assert_kind_of(ActiveModel::Serializer.config.array_serializer, serializer)
           else
             flunk "Unknown association: #{key}"