Remove SessionCookieUpgrader from middleware

This was a transitional bit of code to allow us to rename our session cookies without killing active sessions and logging users out. It's done it's job, the transition is finished, and it isn't doing anything useful now. It can be removed from the middleware stack.

config/application.rb

@@ -34,15 +34,6 @@ end
 
 module Openfoodnetwork
   class Application < Rails::Application
-    config.middleware.insert_before(
-      ActionDispatch::Cookies,
-      SessionCookieUpgrader, {
-        old_key: "_session_id",
-        new_key: "_ofn_session_id",
-        domain: ".#{ENV['SITE_URL'].gsub(/^(www\.)|^(app\.)|^(staging\.)|^(stg\.)/, '')}"
-      }
-    ) if Rails.env.staging? || Rails.env.production?
-
     config.after_initialize do
       # We need this here because the test env file loads before the Spree engine is loaded
       Spree::Core::Engine.routes.default_url_options[:host] = ENV["SITE_URL"] if Rails.env == 'test'