The function works fine, there is a problem in your setup if the function does not remove files. There shall be no symlinks in the real path of a website, so the path /var/www/clients/client1/web1/ may not contain a symlink. If a symlink is detected somewhere in the path, the unlink function has to refuse the removal.
If you moved e.g. /var/www to another disk on your server, then use mount bind instaed of a symlink to point the directory tree to the new location.