message: Remove duplicate definition of discover_callback_t
diff: #include "timeout_handler.h"
  #include "call_every_handler.h"
  #include "thread_pool.h"
  +#include "system.h"
  #include <cstdint>
  #include <functional>
  #include <atomic>
  namespace dronecode_sdk {
  -typedef std::function<void(uint8_t)> discover_callback_t;
  -
  class DronecodeSDKImpl;
  class PluginImplBase;
  