Rails 8.1: use defaults from 8.1, drop interim defaults file

Author: olleolleolle

config/application.rb

@@ -9,7 +9,7 @@
 module Planner
   class Application < Rails::Application
     # Initialize configuration defaults for originally generated Rails version.
-    config.load_defaults 8.0
+    config.load_defaults 8.1
 
     # Please, add to the `ignore` list any other `lib` subdirectories that do
     # not contain `.rb` files, or that should not be reloaded or eager loaded.