Remove the autoload_psr4 before running finalisation.php

[nikosdion]

Replaces #38491

Pull Request for Issue #38486 .

Summary of Changes

Add code in extract.php to remove the administrator/cache/autoload_psr4.php file before loading the finalisation.php as the latter might try to use core code which depends on the former.

Testing Instructions

From Joomla 4.0.0

• Install a Joomla 4.0.0 site
• Replace administrator/components/com_joomlaupdate, components/com_joomlaupdate, media/com_joomlaupdate, and administrator/language/en-GB/com_joomlaupdate.* with the files from this PR.
• Log into the backend
• Do an md5sum of the administrator/cache/autoload_psr4.php file
• Upgrade the site to Joomla 4.2 using the package built from this PR
• Try to access your site's frontend
• Do an md5sum of the administrator/cache/autoload_psr4.php file

From Joomla 4.1.5

• Install a Joomla 4.1.5 site
• Log into the backend
• Do an md5sum of the administrator/cache/autoload_psr4.php file
• Upgrade the site to Joomla 4.2 using the package built from this PR
• Try to access your site's frontend
• Do an md5sum of the administrator/cache/autoload_psr4.php file

Actual result BEFORE applying this Pull Request

The MD5 sums are identical (the autoload_psr4.php file was not removed on update).

Expected result AFTER applying this Pull Request

The MD5 sums are different (the autoload_psr4.php file was removed on update and replaced when accessing your site again).

Documentation Changes Required

None.