Revert "DEV: Migrate existing cookies to Rails 7 format"

This reverts commit 66e8fe9cc63b86ce83b380a2c9563723affefffa as it
unexpectedly caused some users to be logged out. We are investigating
the problem.

lib/middleware/cookies_rotator.rb

@@ -1,34 +0,0 @@
-# frozen_string_literal: true
-
-# Implementing cookies rotator for Rails 7+ as a middleware because this will
-# work in single site mode AND in multisite mode without leaking anything in
-# `Rails.application.config.action_dispatch.cookies_rotations`.
-module Middleware
-  class CookiesRotator
-    def initialize(app)
-      @app = app
-    end
-
-    def call(env)
-      request = ActionDispatch::Request.new(env)
-      env[
-        ActionDispatch::Cookies::COOKIES_ROTATIONS
-      ] = ActiveSupport::Messages::RotationConfiguration.new.tap do |cookies|
-        key_generator =
-          ActiveSupport::KeyGenerator.new(
-            request.secret_key_base,
-            iterations: 1000,
-            hash_digest_class: OpenSSL::Digest::SHA1,
-          )
-        key_len = ActiveSupport::MessageEncryptor.key_len
-
-        cookies.rotate(
-          :encrypted,
-          key_generator.generate_key(request.authenticated_encrypted_cookie_salt, key_len),
-        )
-        cookies.rotate(:signed, key_generator.generate_key(request.signed_cookie_salt))
-      end
-      @app.call(env)
-    end
-  end
-end