[backport] Don't deny smartcards in usb-policy.conf (#6967)

Backport of 651a7b9.

Removing this device class from the USB config would let admins
configure VMs for digital signing purposes.

These devices are also not very useful in Dom0.

Author: contificate

scripts/usb-policy.conf

@@ -20,7 +20,6 @@ ALLOW:vid=056a pid=00fb class=03 # Wacom DTU tablet
 DENY: class=03 subclass=01 prot=01 # HID Boot keyboards
 DENY: class=03 subclass=01 prot=02 # HID Boot mice
 DENY: class=0a # CDC-Data
-DENY: class=0b # Smartcard
 DENY: class=e0 # Wireless controller
 DENY: class=ef subclass=04 # Miscellaneous network devices
 ALLOW: # Otherwise allow everything else