Fix ActivityPub context not being dynamically computed (#11746)

* Fix contexts not being dynamically included

Fixes #11649

* Refactor Note context in serializer

* Refactor Actor serializer

config/initializers/active_model_serializers.rb

@@ -3,22 +3,3 @@ ActiveModelSerializers.config.tap do |config|
 end
 
 ActiveSupport::Notifications.unsubscribe(ActiveModelSerializers::Logging::RENDER_EVENT)
-
-class ActiveModel::Serializer::Reflection
-  # We monkey-patch this method so that when we include associations in a serializer,
-  # the nested serializers can send information about used contexts upwards back to
-  # the root. We do this via instance_options because the nesting can be dynamic.
-  def build_association(parent_serializer, parent_serializer_options, include_slice = {})
-    serializer = options[:serializer]
-
-    parent_serializer_options.merge!(named_contexts: serializer._named_contexts, context_extensions: serializer._context_extensions) if serializer.respond_to?(:_named_contexts)
-
-    association_options = {
-      parent_serializer: parent_serializer,
-      parent_serializer_options: parent_serializer_options,
-      include_slice: include_slice,
-    }
-
-    ActiveModel::Serializer::Association.new(self, association_options)
-  end
-end