Now there is no place use unregister_con_driver,
and we can achieve unregister_con_driver's function
with unregister_con_driver easily, so just delete it
to reduce code size and duplication.
Signed-off-by: NWang YanQing <udknight@gmail.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>