Deletes a key.
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 deletes the key specified by KeyName. If there are multiple versions of the key, all of them are deleted.
Note that the key is only soft-deleted; it can be recovered during the retention period using the RecoverKey method, or permanently deleted using the PurgeKey method. The length of the retention period depends on the configuration of the currently-selected Vault, refer to the Azure Key Vault documentation for more information.