In 3scale 2.5, the Istio integration option will be visible by default (see https://issues.jboss.org/browse/THREESCALE-1900), so customers won't have to do this anymore
https://docs.openshift.com/container-platform/3.11/servicemesh-install/servicemesh-install.html#enabling-service-mesh-for-on-premises-customers

Therefore, the Service Mesh docs should be updated accordingly in the next TP after 3scale 2.5. Basically, what we need is to remove this whole section (the note about SaaS should still be present tho).