drop use of code-generator/generate-groups.sh #2501

Job	Run time
Unit Test (knative/serving)	10m 26s
Unit Test (knative/networking)	4m 46s
Unit Test (knative/eventing)	13m 11s
Unit Test (knative/operator)	6m 58s
Unit Test (knative/client)	7m 25s
Unit Test (knative-extensions/eventing-autoscaler-keda)	5m 23s
Unit Test (knative-extensions/eventing-ceph)	5m 19s
Unit Test (knative-extensions/eventing-github)	5m 49s
Unit Test (knative-extensions/eventing-gitlab)	5m 20s
Unit Test (knative-extensions/eventing-kafka-broker)	9m 52s
Unit Test (knative-extensions/eventing-rabbitmq)	8m 21s
Unit Test (knative-extensions/eventing-redis)	5m 50s
Unit Test (knative-extensions/kn-plugin-admin)	5m 22s
Unit Test (knative-extensions/net-certmanager)	4m 40s
Unit Test (knative-extensions/net-contour)	4m 52s
Unit Test (knative-extensions/net-istio)	5m 39s
Unit Test (knative-extensions/net-kourier)	5m 11s
	1h 54m 24s

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