staging: dgnc: remove sysfs files

The dgnc driver has no business creating "custom" sysfs files just for a
single tty driver.  Combined with the odd way they are created, it's
just a mess, so remove them entirely as I am tired of tripping over them
when doing driver core changes.

Cc: Lidza Louina <lidza.louina@gmail.com>
Cc: Mark Hounschell <markh@compro.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>