Remove parent relations form element serializer

We do not need parent relations like the page and the parent element in
element serializer because usually you render top to bottom.

app/serializers/alchemy/json_api/element_serializer.rb

@@ -16,9 +16,6 @@ class ElementSerializer
         !!element.definition[:deprecated]
       end
 
-      belongs_to :parent_element, record_type: :element, serializer: self
-      belongs_to :page, through: :page_version, record_type: :page, serializer: ::Alchemy::JsonApi::PageSerializer
-
       has_many :essences, polymorphic: true do |element|
         element.contents.map(&:essence)
       end

spec/serializers/alchemy/json_api/element_serializer_spec.rb

@@ -45,10 +45,8 @@
     subject { serializer.serializable_hash[:data][:relationships] }
 
     it "has the right keys and values" do
-      expect(subject[:page]).to eq(data: { id: element.page_id.to_s, type: :page })
       expect(subject[:essences]).to eq(data: element.contents.map { |c| { id: c.essence_id.to_s, type: c.essence.class.name.demodulize.underscore.to_sym } })
       expect(subject[:nested_elements]).to eq(data: [{ id: nested_element.id.to_s, type: :element }])
-      expect(subject[:parent_element]).to eq(data: { id: parent_element.id.to_s, type: :element })
     end
   end
 end