clear retained ota message

main/mqtt_ota.cpp

@@ -85,6 +85,7 @@ void default_ota_event(ota_event_t event) {
         }
         case success:
             ESP_LOGI(TAG, "OTA Successful");
+            publish_message(OTA_FIRMWARE_TOPIC, "");  // clear retained
             break;
         case error:
             ESP_LOGW(TAG, "OTA Error 0x%x", event.error);