docs: ComposerScripts::postUpdate is not needed for end users

It removes system/ThirdParty/Kint/* when running `composer update`
after removing `kint-php/kint` in composer.json.

Author: kenjis

user_guide_src/source/installation/upgrade_430.rst

@@ -77,7 +77,7 @@ composer.json
 =============
 
 If you installed CodeIgnter manually, and are using Composer,
-you need to remove the "kint-php/kint" line, and run ``composer update``.
+you need to remove the following lines, and run ``composer update``.
 
 .. code-block:: text
 
@@ -89,6 +89,13 @@ you need to remove the "kint-php/kint" line, and run ``composer update``.
             ...
         },
         ...
+        "scripts": {
+            "post-update-cmd": [
+                "CodeIgniter\\ComposerScripts::postUpdate"  <-- Remove this line
+            ],
+            "test": "phpunit"
+        },
+        ...
     }
 
 Breaking Changes