Removes all messages marked with 'Deleted' flag from the currently selected mailbox and unselect mailbox.
The 'callback' parameter specifies a function which will be called when the operation completes (or an error is encountered). If the 'callback' parameter is not specified, then the method will block and will not return until the operation completes (or an error is encountered).
The callback for this method is defined as:
'err' is the error that occurred. If there was no error, then 'err' is 'null'.
'err' has 2 properties which hold detailed information:
This method permanently removes all messages that have the 'Deleted' flag set from the current (selected) mailbox, and then closes (deselect) the mailbox.