Update outdated low_processor_usage_mode doc

[jsjtxietian]

For #90774

Should we also remove This is meant for writing applications and editors, but is pretty useless (and can hurt performance) in most games since it mentioned it can be used to save battery

[KoBeWi]

but is pretty useless (and can hurt performance) in most games

I think what this means is that in games there is almost always something moving (even in menu you can have animated background), so low processor mode will have very little effect. Not sure about the performance claim.

[jsjtxietian]

Not sure about the performance claim.

IMHO it means that you will feel laggy if the calculated dynamic_delay is noticeable.

       if (max_fps > 0 && !Engine::get_singleton()->is_editor_hint()) {
		// Override the low processor usage mode sleep delay if the target FPS is lower.
		dynamic_delay = MAX(dynamic_delay, (uint64_t)(1000000 / max_fps));
	}

	if (dynamic_delay > 0) {
		target_ticks += dynamic_delay;
		uint64_t current_ticks = get_ticks_usec();

		if (current_ticks < target_ticks) {
			delay_usec(target_ticks - current_ticks);
		}

		current_ticks = get_ticks_usec();
		target_ticks = MIN(MAX(target_ticks, current_ticks - dynamic_delay), current_ticks + dynamic_delay);
	}

[Mickeon]

It's my whole suggestion so of course I agree.

[akien-mga]

Thanks!