APN lookup fix

tools folder had a reference to ppp-cell-iface.apn-lookup which is removed.
This commit removes the reference to non-existing configuration

Author: Antti Kauppila

tools/test_configs/CellularInterface.json

@@ -34,7 +34,6 @@
             "target.network-default-interface-type": "CELLULAR",
             "nsapi.default-cellular-sim-pin": null,
             "nsapi.dns-response-wait-time": 30000,
-            "ppp-cell-iface.apn-lookup": false,
             "cellular.use-apn-lookup": false,
             "lwip.ipv4-enabled": true,
             "lwip.ipv6-enabled": true,