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.