tools/usb: remove last USBFS user

In commit fb28d58b ("USB: remove CONFIG_USB_DEVICEFS") USBFS got
removed. Since it is gone we can stop using it in testusb and try udev
nodes right away.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>