tube-iface: remove duplicated properties
tube-iface: remove duplicated properties

These wouldn't *have* to disappear, but GObject was complaining
because GabbleTubeIface:connection was implemented in TpBaseChannel as
type TpBaseConnection, when it was expecting a GabbleConnection.

Stop crying, you baby.

Signed-off-by: Jonny Lamb <3d1fb3642aaab2ff70e3392a5ab916bf99eed6a3@collabora.co.uk>

Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,Ziemin/telepathy-gabble,mlundblad/telepathy-gabble,mlundblad/telepathy-gabble,mlundblad/telepathy-gabble