Merge #276 broke downstream packages

[jmachowinski]

Hi, the recent merge of 'Expose callback groups - backport to iron' (https://github.com/ros-perception/image_common/pull/276) just broke donwstream packages (e.g. https://github.com/RobotWebTools/web_video_server) , as

  Subscriber subscribe(
    const std::string & base_topic, uint32_t queue_size,
    void (* fp)(const ImageConstPtr &),
    const TransportHints * transport_hints = nullptr)

and

  Subscriber subscribe(
    const std::string & base_topic, uint32_t queue_size,
    void (* fp)(const ImageConstPtr &),
    const TransportHints * transport_hints = nullptr,
    const rclcpp::SubscriptionOptions options = rclcpp::SubscriptionOptions())

are ambiguous.

[jmachowinski]

Recent merges fixed the issue