Deletes a key.
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.