Update extensions.md

Removing duplicate Defender for Cloud Link

Author: tmanley7m

articles/azure-arc/kubernetes/extensions.md

@@ -311,7 +311,6 @@ Learn more about the cluster extensions currently available for Azure Arc-enable
 * [Azure Monitor](../../azure-monitor/containers/container-insights-enable-arc-enabled-clusters.md?toc=/azure/azure-arc/kubernetes/toc.json)
 * [Microsoft Defender for Cloud](../../security-center/defender-for-kubernetes-azure-arc.md?toc=/azure/azure-arc/kubernetes/toc.json)
 * [Azure Arc-enabled Open Service Mesh](tutorial-arc-enabled-open-service-mesh.md)
-* [Microsoft Defender for Cloud](../../security-center/defender-for-kubernetes-azure-arc.md?toc=/azure/azure-arc/kubernetes/toc.json)
 * [Azure App Service on Azure Arc](../../app-service/overview-arc-integration.md)
 * [Event Grid on Kubernetes](../../event-grid/kubernetes/overview.md)
 * [Azure API Management on Azure Arc](../../api-management/how-to-deploy-self-hosted-gateway-azure-arc.md)