docs: add note to upgrade_420.rst

Author: kenjis

user_guide_src/source/installation/upgrade_420.rst

@@ -43,6 +43,8 @@ The constants ``EVENT_PRIORITY_LOW``, ``EVENT_PRIORITY_NORMAL`` and ``EVENT_PRIO
 composer.json
 =============
 
+.. note:: This procedure is not required in v4.5.0 or later.
+
 If you use Composer, when you installed CodeIgniter v4.1.9 or before, and
 if there are ``App\\`` and ``Config\\`` namespaces in your ``/composer.json``'s ``autoload.psr-4``
 like the following, you need to remove these lines, and run ``composer dump-autoload``.