Fixed chat commands crashing replays

This does not just fix #5755, but also the fact that chat commands were sent also via a regular chat order so they would be executed on *all* clients who read the chat and watch them for strings starting with `/`. It just crashed because on replays the local client is null, but in fact this is a serious exploit especially in combination with https://github.com/OpenRA/OpenRA/pull/5701! We also don't need to send a new Order.Chat and hide the received output later, because all Chat/Player/DevCommands issue proper network orders themselves once invoked.