staging:iio: remove num_interrupt_lines from documentation

Commit 5aa9618 ("staging:iio: remove broken support for
multiple event interfaces.") removed the num_interrupt_lines field from
struct iio_info but the documentation was never updated.

Signed-off-by: Johan Hovold <jhovold@gmail.com>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/iio/Documentation/device.txt

@@ -29,8 +29,6 @@ Then fill in the following:
 	* info->driver_module:
 		Set to THIS_MODULE. Used to ensure correct ownership
 		of various resources allocate by the core.
-	* info->num_interrupt_lines:
-		Number of event triggering hardware lines the device has.
 	* info->event_attrs:
 		Attributes used to enable / disable hardware events.
 	* info->attrs: