Client: Simplify client struct definition

src/client/ua_client_internal.h

@@ -173,8 +173,8 @@ struct UA_Client {
     /* Subscriptions */
 #ifdef UA_ENABLE_SUBSCRIPTIONS
     UA_UInt32 monitoredItemHandles;
-    LIST_HEAD(ListOfUnacknowledgedNotifications, UA_Client_NotificationsAckNumber) pendingNotificationsAcks;
-    LIST_HEAD(ListOfClientSubscriptionItems, UA_Client_Subscription) subscriptions;
+    LIST_HEAD(, UA_Client_NotificationsAckNumber) pendingNotificationsAcks;
+    LIST_HEAD(, UA_Client_Subscription) subscriptions;
     UA_UInt16 currentlyOutStandingPublishRequests;
 #endif