File component upload description should be skipped if $filter === FALSE

The $filter argument in _webform_render_file() and other _webform_render_* callbacks is used by Form Builder to generate a raw editable version of the element. Right now we're adding the file upload help all the time, making it so if you edit a file component with Form Builder, you end up editing the file upload help. Every time you edit, more help gets appended to the description. This description should not be part of the editable configuration, so it should be skipped when $filter === FALSE.