General: Remove unused dynamic `$features` variable from the constructor of `class-ftp.php`.

This fixes a PHP 8.2 deprecation, by removing the dynamic `$features` property from the ftp class as it is not used anywhere.

Props kmurphyzuora, debarghyabanerjee, hellofromTonya, peter8nss.
Fixes #62159.



git-svn-id: https://develop.svn.wordpress.org/trunk@62059 602fd350-edb4-49c9-b593-d223f7449a82