Remove dupicate Mesos constructor

// TODO(vinod): Remove this in favor of the below constructor.
Mesos(const std::string& master,
      const std::function<void(void)>& connected,
      const std::function<void(void)>& disconnected,
      const std::function<void(const std::queue<Event>&)>& received);

Mesos(const std::string& master,
      ContentType contentType,
      const std::function<void(void)>& connected,
      const std::function<void(void)>& disconnected,
      const std::function<void(const std::queue<Event>&)>& received);