To cleanup, follow the below steps.
To remove telemetry configuration / port-forward process
kubectl delete -f istio-telemetry.yaml
To remove the application virtual services / destination rules
kubectl delete -f samples/bookinfo/networking/virtual-service-all-v1.yaml
kubectl delete -f samples/bookinfo/networking/destination-rule-all.yaml
To remove the gateway / application
kubectl delete -f samples/bookinfo/networking/bookinfo-gateway.yaml
kubectl delete -f samples/bookinfo/platform/kube/bookinfo.yaml
To remove Istio
helm delete --purge istio
helm delete --purge istio-init