examples: Fix broken python examples after wifi api cleanup

examples/wireless/mixed-wired-wireless.py

@@ -257,7 +257,7 @@ def main(argv):
         #  Create another ad hoc network and devices
         # 
         ssid = ns.wifi.Ssid('wifi-infra' + str(i))
-        wifiInfra = ns.wifi.WifiHelper.Default()
+        wifiInfra = ns.wifi.WifiHelper()
         wifiPhy.SetChannel(wifiChannel.Create())
         wifiInfra.SetRemoteStationManager('ns3::ArfWifiManager')
         macInfra = ns.wifi.WifiMacHelper();

examples/wireless/wifi-ap.py

@@ -104,7 +104,7 @@ def main(argv):
     # disable fragmentation
     ns.core.Config.SetDefault("ns3::WifiRemoteStationManager::FragmentationThreshold", ns.core.StringValue("2200"))
 
-    wifi = ns.wifi.WifiHelper.Default()
+    wifi = ns.wifi.WifiHelper()
     mobility = ns.mobility.MobilityHelper()
     stas = ns.network.NodeContainer()
     ap = ns.network.NodeContainer()

src/flow-monitor/examples/wifi-olsr-flowmon.py

@@ -49,7 +49,7 @@ def main(argv):
 
     cmd.Parse(argv)
 
-    wifi = ns.wifi.WifiHelper.Default()
+    wifi = ns.wifi.WifiHelper()
     wifiMac = ns.wifi.WifiMacHelper()
     wifiPhy = ns.wifi.YansWifiPhyHelper.Default()
     wifiChannel = ns.wifi.YansWifiChannelHelper.Default()