contactmodel: remove useless addContact call

This line is not justified anymore as the daemon seems to emit
everytime the contactAdded signal.
Indeed, this line is fixed by
ring-daemon/1353a641fc064b39a3414ab0cd074dd0ebfcb54c

Change-Id: I94e3b0bdf76658749b70affb847130f843a5dc09
Reviewed-by: Andreas Traczyk <andreas.traczyk@savoirfairelinux.com>