tty: remove dtr/rts use from the driver open methods

These are handled by the tty_port core code which will raise and lower the
carrier correctly in tty_wait_until_ready

Signed-off-by: Alan Cox <alan@linux.intel.com>
Cc: stable <stable@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>