Issue #2299457 by alexpott: remove unused UnsupportedConfigDataTypeException.

core/lib/Drupal/Core/Config/UnsupportedConfigDataTypeException.php

-<?php
-
-/**
- * @file
- * Contains \Drupal\Core\Config\UnsupportedConfigDataTypeException.
- */
-
-namespace Drupal\Core\Config;
-
-/**
- * Exception thrown when a config data type is invalid.
- */
-class UnsupportedConfigDataTypeException extends ConfigException {
-}