Remove prepend conditional from RouteWrapper patch

Module#prepend was added in ruby 2.0, and the required ruby version is
2.5+

The Rails > 4 conditional will also always be true since the required
Rails version is 5.2+

Author: skipkayhil

lib/sprockets/rails/route_wrapper.rb

@@ -1,23 +1,13 @@
 module Sprockets
   module Rails
     module RouteWrapper
-
       def internal_assets_path?
         path =~ %r{\A#{self.class.assets_prefix}\z}
       end
 
       def internal?
         super || internal_assets_path?
       end
-
-      def self.included(klass)
-        klass.class_eval do
-          def internal_with_sprockets?
-            internal_without_sprockets? || internal_assets_path?
-          end
-          alias_method_chain :internal?, :sprockets
-        end
-      end
     end
   end
 end

lib/sprockets/railtie.rb

@@ -232,11 +232,7 @@ def self.build_manifest(app)
       ActionDispatch::Routing::RouteWrapper.class_eval do
         class_attribute :assets_prefix
 
-        if defined?(prepend) && ::Rails.version >= '4'
-          prepend Sprockets::Rails::RouteWrapper
-        else
-          include Sprockets::Rails::RouteWrapper
-        end
+        prepend Sprockets::Rails::RouteWrapper
 
         self.assets_prefix = config.assets.prefix
       end