This proposed patch add support for deleting usb devices by providing the (exact) same string they were added with, thus enabling to remove a usb device with the host string. The old capability of deleting usb device by their internal port is not harmed.
I had to move USBHostDevice to vl.h so that I will be able to reference it from vl.c
and last, I've changed the output of info usb so that it will include the saved string (for reference).