Plank is still looking for GKE cluster

[irbekrm]

We removed gke cluster from Prow's config, but it appears like plank is still looking for it and throwing errors:

{"component":"plank","error":"errors syncing: [error starting pod : unknown cluster alias \"gke\" error starting pod : unknown cluster alias \"gke\" error starting pod : unknown cluster alias \"gke\" error starting pod : unknown cluster alias \"gke\"]","file":"prow/plank/controller.go:170","func":"k8s.io/test-infra/prow/plank.(*Controller).Start","level":"error","msg":"Error syncing.","severity":"error","time":"2021-05-28T08:27:58Z"}
{"component":"plank","duration":"57.521714ms","file":"prow/plank/controller.go:172","func":"k8s.io/test-infra/prow/plank.(*Controller).Start","level":"info","msg":"Synced","severity":"info","time":"2021-05-28T08:27:58Z"}
{"component":"plank","error":"errors syncing: [error starting pod : unknown cluster alias \"gke\" error starting pod : unknown cluster alias \"gke\" error starting pod : unknown cluster alias \"gke\" error starting pod : unknown cluster alias \"gke\"]","file":"prow/plank/controller.go:170","func":"k8s.io/test-infra/prow/plank.(*Controller).Start","level":"error","msg":"Error syncing.","severity":"error","time":"2021-05-28T08:28:28Z"}
{"component":"plank","duration":"34.927807ms","file":"prow/plank/controller.go:172","func":"k8s.io/test-infra/prow/plank.(*Controller).Start","level":"info","msg":"Synced","severity":"info","time":"2021-05-28T08:28:28Z"}

See related discussion on Slack https://kubernetes.slack.com/archives/CDEQJ0Q8M/p1622138455202100

[irbekrm]

Appears like this happened because there were some old 'periodic' Prowjobs with the old version of kubeconfig- deleting those seems to have fixed the issue.