Avoid overwriting the pre-existing kubectl

Kubectl is already provided in GitHub Actions' virtual environments (for Ubuntu & Windows at least). It is always of the latest version. There is no need to override it with our own kubectl. If needed, this can be implemented explicitly by those who need it.

action.sh

@@ -87,12 +87,6 @@ echo "::set-output name=k8s-version::${K8S}"
 curl --silent --fail https://raw.githubusercontent.com/rancher/k3d/main/install.sh | bash
 k3d cluster create ${K3D_NAME:-} --wait --image=rancher/k3s:"${K3S//+/-}" ${K3D_ARGS:-}
 
-# Install kubectl (for this action only, not for the whole job).
-curl --silent --fail -L -o kubectl \
-  https://storage.googleapis.com/kubernetes-release/release/"$K8S"/bin/linux/amd64/kubectl
-chmod +x kubectl
-sudo mv kubectl /usr/local/bin/
-
 # Sometimes, the service account is not created immediately. Nice trick, but no:
 # we need to wait until the cluster is fully ready before starting the tests.
 if [[ -z "${SKIP_READINESS}" ]]; then