upload.module now remembers values of checkboxes, so no need for private_upload.module to do so

#173656: Erratic checkbox behaviour for uploads fixed the core bug where Drupal didn't remember the values of the "remove" and "list" checkboxes; private_uploads included a fix for this which is now unnecessary. In fact, it has a comment which reads:

// While I am here lets fix the problem with delete and list as well.
// Q: Do I still need this fix in D6?