All XML APIs have been removed

The Media module provided a set of APIs for storing and retrieving XML files. In order to improve performance and streamline the Media module, the XML APIs have been removed.

These APIs are not used by the Media module itself and were not fully featured enough to be adopted by more than a handful of media provider modules. Any provider modules that did rely on the XML APIs are encouraged to create their own database tables for storing XML files and include their own copies of any of the XML API functions that they relied on.

See #2068017: Use own XML functions to allow XML APIs to be removed from Media for an example of how the Media:YouTube provider module accommodated the removal of the XML APIs.