Update index.yml

Removed the Preview label from Azure IoT Operations

Author: eross-msft

articles/iot/index.yml

@@ -44,7 +44,7 @@ highlightedContent:
       itemType: concept
       url: ../digital-twins/concepts-models.md
     # Card
-    - title: Azure IoT Operations (Preview)
+    - title: Azure IoT Operations
       itemType: overview
       url: ../iot-operations/get-started/overview-iot-operations.md