ezpublish_legacy/var/cache/active_extension_*.php are not being cleaned if you clean the caches with purge, leaving old files behind.

Steps to Reproduce

1. Generate autoloads
2. execute "ls ezpublish_legacy/var/cache/" to see the existing "active_extension_*.php" files
3. In the backoffice, remove an active extension and regenerate autloads
4. execute "ls ezpublish_legacy/var/cache/" to see the existing "active_extension_*.php" files

The old files still exist. Try to clean the files with purge and confirm they won't be deleted