usbguard: 0.7.4 -> 0.7.5

https://github.com/USBGuard/usbguard/releases/tag/usbguard-0.7.5

* no longer needs/uses qt as of 0.7.5
* asciidoctor -> asciidoc, drop pandoc
  (pandoc only seems to be used as part of doc spell-check
   which we don't enable anyway)
* docbook bits