WiFiInterface: remove connect implementation

We do not want to mix Ethernet and Wifi at the moment, thus WiFiInterface
should implement own connect using emac.

features/net/network-socket/WiFiInterface.cpp

@@ -60,12 +60,3 @@ int WiFiInterface::set_credentials(const char *ssid, const char *pass, nsapi_sec
     return 0;
 }
 
-int WiFiInterface::connect()
-{
-    if (!_ssid || !_pass) {
-        return NSAPI_ERROR_PARAMETER;
-    }
-
-    return connect(_ssid, _pass, _security);
-}
-