Remove channel type related properties
Remove channel type related properties

Remove the "type" and "channel-type" properties. Reimplement their getters in a
different way.

freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control,freedesktop-unofficial-mirror/telepathy__telepathy-mission-control