After setting a static ip address in a debian based os, there is often a secondary ip address visible with ip addr show. This is caused by the dhcpcd service which keeps running after setting a static ip. Stopping this service will remove the secondary ip address after a reboot or network restart.
update-rc.d dhcpcd disable
service dhcpcd stop
#and optionally the next line or a reboot
ip addr del %YOURS-SECOND-IP% dev ethX
Replace %YOURS-SECOND-IP% with the unwanted secondary ip address. And replace ethx with the interface name. Restart the network. Or just reboot and the secondary ip will be gone.
Works on a Volumio based Raspberry Pi and Ubuntu Server 18.04.2 LTS.