The control file for vyatta-cfg-firewall says that it replaces vyatta-cfg-system, vyatta-openvpn and vyatta-wirelessmodem
https://github.com/vyos/vyatta-cfg-firewall/blob/current/debian/control
This line was added on 29 Apr 2009:
https://github.com/vyos/vyatta-cfg-firewall/commit/d33af167d65047adcd418bef5f7483168ecb8494
@runrar says: "the policy about upgrading vyos is for now upgrade by installing new image, so the issue in the commit from 09 is non-existant i think."