remove IAX account and usage of libiax

Issue generated from Tuleap's migration script. Originally submitted by: Guillaume Roguez (guillaume)

libiax in current form has a licence not compatible with our GPLv3 licence.
As IAX account has not been updated and no more support is done on it since first Ring release,
and there is no significant usage of it in the community, the Ring Team has decided to remove it from sources.

daemon, lrc and all clients are impacted by this ticket.