In hindsight, the NMVpnPluginOld should never have made public for
nm-1-0 as there are no users and we don't want to support this API.
For now, just deprecate it.
The new VPN plugin API will hopefully simplify some the the tasks that
are currently handled by nm-vpn-plugin-utils functions, so make those
functions explicitly be part of the "old" API. (If we still want them
in the new API we can just move them back out, and have the "_old_"
versions just be wrappers around the undeprecated ones.)
Rename libnm's NMVpnPlugin to NMVpnPluginOld, in preparation for
having a new-and-improved NMVpnPlugin in NM 1.2. Also remove it from
NM-1.0.gir.
Make nm-vpn-plugin-old.h be separately includable, since it's not
included from NetworkManager.h, and we probably don't want it to be.
Remove NMVpnPlugin, NMVpnPluginUiInterface, and nm-vpn-plugin-utils
from the docs, since they're basically undocumented anyway.
