Hi blackone!
Synaptic and update-notifier were included in the release candidate, but are not recommended to use (rather for testing purposes). So the simplest solution would be just to remove/purge these packages by 'apt-get purge synaptic update-notifier', although it shouldn't do any harm as they are just gui frontends for apt-get to fetch and install available updates. After that (at least after a re-login) the icon in the panel should have disappeared.