You can't really do that unless you edit the template to not allow that option to be selected. I think you just need to remove it from the album_edit template:
HTML Code:
<li><label for="rb_albumtype_private"><input type="radio" id="rb_albumtype_private" name="albumtype" value="private" {vb:raw formdata.albumtype_private} tabindex="1" /> {vb:rawphrase private}</label><p class="description">{vb:rawphrase private_only_visible_contacts_moderators}</p></li>