Makes sense to remove a useless privacy feature when many sites just ignore DNT requests. I'd rather not have them waste time on maintaining a feature that is only useful on a handful of sites that actually respect it.

Do not track never worked, because it let the website operators decide if they want to honor it, and there was no downside to ignoring it.

Is it set by default now or just totally removed?

if they really cared about tracking they'd include noscript in every browser.