Revert azure-cni-v1 prow template to Ubuntu (default OS)

Azure CNI v1 + Azure Linux 4 causes the control plane to become
unreachable externally: the node boots and kubeadm init succeeds
locally, but the node drops off the network ~10 minutes after boot,
preventing the cluster from reaching ControlPlaneInitialized. The
same AzL4 setup scripts work fine with Calico-based flavors (spot,
custom-vnet), so this appears to be an incompatibility between Azure
CNI v1's host-NIC reconfiguration and Azure Linux 4.

Keep azure-cni-v1 on the default Ubuntu CI image for now; only the
Calico-based spot and custom-vnet flavors default to Azure Linux 4.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: mboersma

templates/test/ci/cluster-template-prow-azure-cni-v1.yaml

@@ -11,23 +11,6 @@ patches:
 - path: ../patches/tags.yaml
 - path: ../patches/controller-manager.yaml
 - path: ../patches/cluster-label-cloud-provider-azure.yaml
-- path: ../patches/azl4-azuremachinetemplate-image.yaml
-- path: ../patches/azl4-remove-marketplace-image.yaml
-- path: ../patches/azl4-kubeadmcontrolplane-setup.yaml
-  target:
-    group: controlplane.cluster.x-k8s.io
-    kind: KubeadmControlPlane
-    name: .*-control-plane
-    version: v1beta1
-- path: ../patches/azl4-kubeadmconfigtemplate-setup.yaml
-  target:
-    group: bootstrap.cluster.x-k8s.io
-    kind: KubeadmConfigTemplate
-    name: .*-md-0
-    namespace: default
-    version: v1beta1
-- path: ../patches/azl4-cloud-provider-azure-cacertdir.yaml
-- path: ../patches/azl4-cloud-provider-azure-ci-cacertdir.yaml
 
 sortOptions:
   order: fifo