⚙️ Utilize Hyrax's schema search paths config

As of Hyrax `9d8d5f8`, there is now a configuration for the
`Hyrax::SimpleSchemaLoader` that allows us to do away with the need for
a decorator.  I'm leaving it there for applications that aren't at
`9d8d5f8` yet but guard it.

Ref:
  - samvera/hyrax@9d8d5f8

app/services/iiif_print/simple_schema_loader_decorator.rb

@@ -9,4 +9,4 @@ def config_search_paths
  end
  end
 end
-Hyrax::SimpleSchemaLoader.prepend(IiifPrint::SimpleSchemaLoaderDecorator)
+Hyrax::SimpleSchemaLoader.prepend(IiifPrint::SimpleSchemaLoaderDecorator) unless Hyrax.config.respond_to?(:simple_schema_loader_config_search_paths)

lib/iiif_print/engine.rb

@@ -65,6 +65,8 @@ class Engine < ::Rails::Engine
  config.callback.set(:after_create_fileset) do |file_set, user|
  IiifPrint.config.handle_after_create_fileset(file_set, user)
  end
+
+ config.simple_schema_loader_config_search_paths += [IiifPrint::Engine.root]
  end
  end
  # rubocop:enable Metrics/BlockLength