USB: usbip: remove CONFIG_USB_DEBUG reference

As the config option is gone, it's a bit hard to enable it so remove the
reference to it.
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/staging/usbip/userspace/README

@@ -195,7 +195,6 @@ Detach the imported device:
     - Shutdown firewall.
 	- usbip now uses TCP port 3240.
     - Disable SELinux.
-    - If possible, compile your kernel with CONFIG_USB_DEBUG flag and try again.
     - Check the kernel and daemon messages.