NMRemoteConnection had two DBusGConnection properties
(NMRemoteConnection:bus and NMRemoteConnection:dbus-connection) and
two D-Bus path properties (NMConnection:path and
NMRemoteConnection:dbus-path). The former of each pair were the
traditional names, and the latter were added for compatibility with
NMObject.

In libnm, we can just drop NMRemoteConnection:bus, and use the
NMObject-compatible :dbus-connection name instead.

For the path properties, we need to rename either NMConnection:path or
NMObject:dbus-path. Since NMObject already has "nm_object_get_path()"
rather than "nm_object_get_dbus_path()", and it already mistakenly
referred to the property as "NMObject:path" in the gtk-docs, it seemed
to make sense to rename that one rather than the NMConnection one.

(And then, for consistency, rename "nm_object_get_connection()" to
"nm_object_get_dbus_connection()" to also match its property.)