Remove obsolete backport from Rails 7 (#26254)

lib/action_controller/conditional_get_extensions.rb

@@ -1,15 +0,0 @@
-# frozen_string_literal: true
-
-module ActionController
-  module ConditionalGetExtensions
-    def expires_in(*)
-      # This backports a fix from Rails 7 so that a more private Cache-Control
-      # can be overriden by calling expires_in on a specific controller action
-      response.cache_control.delete(:no_store)
-
-      super
-    end
-  end
-end
-
-ActionController::ConditionalGet.prepend(ActionController::ConditionalGetExtensions)