vt: delete unneeded function bind_con_driver

Now there is no place use bind_con_driver,
and do_bind_con_driver can achieve bind_con_driver's
function easily, so just delete it to reduce code size and
duplication.

Signed-off-by: Wang YanQing <udknight@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>