Fired before a file item in the upload list is being removed.
The event object receives the following additional properties:
files- a list of File objects in the current selection operation. Each file contains:
name- the name of the file
size- the size of the file in bytes
type- the file's MIME type
status- the current status of the item - "pending", "uploading", "complete", "removing" or "error".
This event can be cancelled.