chizhg: Do not set --workload-pool when creating GKE autopilot clusters

JobBuild
158
07-26 18:30
pull-kubetest2-build 1419726717026570240
pull-kubetest2-gke-up-down-multicluster 1419726716951072768
pull-kubetest2-gke-up-down-singlecluster 1419726716904935424
pull-kubetest2-verify 1419726716997210112