staging:iio:events: Remove obsolete documentation

Commit 43ba1100 ("staging:iio:events: Use waitqueue lock to protect event
queue") removed the event_list_lock field from the iio_event_interface struct,
but missed to remove the same field from the documentation for that function.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/iio/industrialio-event.c

@@ -28,7 +28,6 @@
 /**
  * struct iio_event_interface - chrdev interface for an event line
  * @wait:		wait queue to allow blocking reads of events
- * @event_list_lock:	mutex to protect the list of detected events
  * @det_events:		list of detected events
  * @dev_attr_list:	list of event interface sysfs attribute
  * @flags:		file operations related flags including busy flag.