usb-host: rip out legacy procfs support

usb-host: rip out legacy procfs support

This patch removes support for parsing /proc/bus/usb/devices for device
discovery.  The code lacks a few features compared to the sysfs code and
is also bitrotting as everybody has sysfs these days.

This implies having sysfs mounted is mandatory now to use the usb-host
driver.  udev isn't required though.  qemu will prefer the udev-managed
device nodes below /dev/bus/usb, but in case this directory isn't preset
qemu will use the device nodes below /proc/bus/usb (default usbfs mount
point).

Bottom line: make sure you have both sysfs and usbfs mounted properly,
and everything should continue to work as it did before.

Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>