phonedirectory: Add more explicit support for deduplicated RingId

This commit complements the previous one. Now that Ring CMs are
properly deduplicated once their registeredName is validated,
disable the old entry in the debug model.

It also foward the deduplication signal to the RecentModel/Timeline
can also take notice. This greatly simplify the code.

Change-Id: I4e8839744d0eb12aa32f4bf6a8a50f7e0cc51d88
Reviewed-by: Nicolas Jäger <nicolas.jager@savoirfairelinux.com>