This was only ever added for gnome-software, and is too inflexible for anything
else. It turns out we don't even need it in GNOME, as we can construct a
suitable ID ourselves using the existing values.
It was also ambiguous whether the unique ID was in reference to the device
or release -- and for gnome-software we need both.
This allows us to show the devices in a GUI with a nice icon. Some of the icon
mappings are not perfect and I'll be asking the GNOME designers for some
additions to the icon specification.
Custom vendor icons can also be specified, and /usr/share/fwupd/icons would be
a good place to put them. If vendor icons are used they should show a physical
device with the branding, rather than just the vendor logo.
This functionality is required so that AppStream metadata can check the fwupd
version, the firmware version, bootloader version or a combination of all three.