message: follow_me: remove unnecessary unlock
diff: @@ -337,7 +337,6 @@ void FollowMeImpl::process_heartbeat(const mavlink_message_t& message)
  } else if (follow_me_active && _mode == Mode::NOT_ACTIVE) {
  // We're in FollowMe mode now
  _mode = Mode::ACTIVE;
  - _mutex.unlock(); // we must unlock to avoid deadlock in send_target_location()
  return;
  }
  }
  