Future metadata from the LVFS will set the protocol the firmware is expected to
use. As vendors love to re-use common terms like DFU for incompatible protocols,
namespace them with the controlling company ID with an approximate reverse DNS
namespace.
This also allows more than one plugin to define support for the same protocol,
for instance rts54hid+rts54hub and synapticsmst+dell-dock.
This was compiling and passing CI as the un-implemented legacy functionality
was still exported in the header.
Remove the prototypes for the missing symbols and fix up the plugin.
