refactor(device): drop the _unifying suffix inside probe/unifying

bolt.rs has drain_device_arrival and read_codename; unifying.rs had the same helpers with a _unifying suffix that the module path already spells, and parse_codename_unifying beside them. The suffix is gone, and the two comments that named the old function — the replay slot model and hidpp's receiver register enum, which also still said inventory.rs — point at the module.