Remove XML support

XML support in Neutron has always been a second class feature to the
JSON API and broken for many extensions and outputs. The XML API been marked as
deprecated for the Icehouse and Juno release and is ready for removal in
Kilo.

Change-Id: I611aa9382ba3bfb08b2970c63e83b0fdd3d2e8a4
Closes-Bug: #1380787
Merge "Remove XML support"