eknc-subtree-dispatcher: use G_DEFINE_TYPE_WITH_PRIVATE
eknc-subtree-dispatcher: use G_DEFINE_TYPE_WITH_PRIVATE

I staged a change I didn't mean to and made this G_DEFINE_TYPE
https://phabricator.endlessm.com/T13418

endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib,endlessm/eos-knowledge-lib