Document @return value for wp_unschedule_event().

See #33475.

git-svn-id: https://develop.svn.wordpress.org/trunk@34044 602fd350-edb4-49c9-b593-d223f7449a82

src/wp-includes/cron.php

@@ -161,6 +161,7 @@ function wp_reschedule_event( $timestamp, $recurrence, $hook, $args = array() )
  * Although not passed to a callback function, these arguments are used
  * to uniquely identify the scheduled event, so they should be the same
  * as those used when originally scheduling the event.
+ * @return false|void False when an event is not unscheduled.
  */
 function wp_unschedule_event( $timestamp, $hook, $args = array() ) {
 	// Make sure timestamp is a positive integer