Remove `utils.last_octet`
Remove `utils.last_octet`

Not used since 142f6f6d3e7ce63e0a34cf68c8473d047766e093 (over 3 years ago!)

Change-Id: I2a98c38682aabd8ef8cad8151075f8ea64dbead8

openstack/oslo.versionedobjects,citrix-openstack-build/oslo.versionedobjects