Revert #6923: start_date parameter is no longer in use

There was an issue with the start_date parameter for AIs. It did not let Random AIs to have their configure button clickable once the game has started, and this was due to the start_date not being pushed into the config.

But now that start_date is no longer in use since #10653, this workaround can be safely removed.

src/openttd.cpp

@@ -358,9 +358,6 @@ void MakeNewgameSettingsLive()
 		_settings_game.ai_config[c] = nullptr;
 		if (_settings_newgame.ai_config[c] != nullptr) {
 			_settings_game.ai_config[c] = new AIConfig(_settings_newgame.ai_config[c]);
-			if (!AIConfig::GetConfig(c, AIConfig::SSS_FORCE_GAME)->HasScript()) {
-				AIConfig::GetConfig(c, AIConfig::SSS_FORCE_GAME)->Change(std::nullopt);
-			}
 		}
 	}
 	_settings_game.game_config = nullptr;