Use Rails 7.1 cache format

Just like we mentioned in commit 001eee3d6, according to the Rails
configuration guide [1], with this format, Rails serializes cache
entries more efficiently. Most importantly:

> All formats are backward and forward compatible, meaning cache entries
> written in one format can be read when using another format. This
> behavior makes it easy to migrate between formats without invalidating
> the entire cache.

[1] https://guides.rubyonrails.org/v7.1/configuring.html#config-active-support-cache-format-version

config/initializers/new_framework_defaults_7_1.rb

@@ -216,21 +216,6 @@ Rails.application.config.active_record.commit_transaction_on_non_local_return =
 #++
 Rails.application.config.active_record.generate_secure_token_on = :initialize
 
-###
-# ** Please read carefully, this must be configured in config/application.rb **
-#
-# Change the format of the cache entry.
-#
-# Changing this default means that all new cache entries added to the cache
-# will have a different format that is not supported by Rails 7.0
-# applications.
-#
-# Only change this value after your application is fully deployed to Rails 7.1
-# and you have no plans to rollback.
-# When you're ready to change format, add this to `config/application.rb` (NOT
-# this file):
-#   config.active_support.cache_format_version = 7.1
-
 
 ###
 # Configure Action View to use HTML5 standards-compliant sanitizers when they are supported on your