message: dronecore: make `device()` interface clearer
diff: @@ -86,7 +86,7 @@ public:
  const std::vector<uint64_t> &device_uuids() const;
  /**
  - * Return the only discovered device.
  + * Return the first discovered device.
  *
  * This returns the first discovered device or a null device if no device has yet been found.
  *
  