eventLeave
Triggered when on a calendar when one if its events is about to be dropped onto another calendar.
function( info ) { }
info is a plain object with the following properties:
| event | 
       An Event object that is about to leave.  | 
|---|---|
| relatedEvents | an array of other related Event Objects that also left. an event might have other recurring event instances or might be linked to other events with the same groupId | 
| revert | a function that can be called to reverse this action | 
| view | 
       The current View Object.  | 
| draggedEl | 
       The HTML element that was being dragged.  | 
This callback will be fired before the receiving calendar’s drop and eventReceive callbacks are fired.
This callback is fired before eventRemove.