Fix: libcrmcommon: Drop xmlRegisterNodeDefault()
...and xmlDeregisterNodeDefault().
Within libxml2, these are tagged with the "deprecated" compiler
attribute, causing builds on some bleeding-edge distributions (currently
at least debian-experimental) to fail.
Instead, allocate and free private data as needed when creating and
freeing XML nodes.
Fixes T838
Signed-off-by: Reid Wahl <nrwahl@protonmail.com>