Optimize file path to class name conversion (#3589)

Author: bnix

lib/rails_admin/config.rb

@@ -364,19 +364,16 @@ def visible_models(bindings)
 
     private
 
-      def lchomp(base, arg)
-        base.to_s.reverse.chomp(arg.to_s.reverse).reverse
-      end
-
       def viable_models
         included_models.collect(&:to_s).presence || begin
           @@system_models ||= # memoization for tests
             ([Rails.application] + Rails::Engine.subclasses.collect(&:instance)).flat_map do |app|
               (app.paths['app/models'].to_a + app.config.eager_load_paths).collect do |load_path|
                 Dir.glob(app.root.join(load_path)).collect do |load_dir|
+                  path_prefix = "#{app.root.join(load_dir)}/"
                   Dir.glob("#{load_dir}/**/*.rb").collect do |filename|
                     # app/models/module/class.rb => module/class.rb => module/class => Module::Class
-                    lchomp(filename, "#{app.root.join(load_dir)}/").chomp('.rb').camelize
+                    filename.delete_prefix(path_prefix).chomp('.rb').camelize
                   end
                 end
               end