simplify RailsBooter no need to account for old Rails

Author: kares

src/main/ruby/jruby/rack/rails/environment.rb

@@ -26,12 +26,22 @@ def boot!
       super
       ENV['RAILS_ROOT'] = app_path
       ENV['RAILS_ENV'] = rails_env
+      self
+    end
 
-      require 'jruby/rack/rails/environment'
-      extend RailsEnvironment
+    # @return [Rails::Application] the (loaded) application instance
+    def to_app
+      # backward "compatibility" calling #to_app without a #load_environment
+      load_environment
+      ::Rails.application
+    end
 
-      set_public_root
-      self
+    # Loads the Rails environment (*config/environment.rb*).
+    def load_environment
+      require expand_path('config/boot.rb')
+      require 'jruby/rack/rails/railtie'
+      require expand_path('config/environment.rb')
+      require 'jruby/rack/rails/extensions'
     end
 
     protected
@@ -42,12 +52,6 @@ def set_relative_url_root
       end
     end
 
-    # @see JRuby::Rack::RailsBooter::Rails2Environment#set_public_root
-    # @see JRuby::Rack::RailsBooter::Rails3Environment#set_public_root
-    def set_public_root
-      # no-op by default - leave as it is
-    end
-
     # @deprecated no longer used, replaced with {#run_boot_hooks}
     def load_extensions
       # no-op