Adobe must have changed their mind, and decided to switch to coding in the width and height... which I think is actually is a good change for the following reasons:
- Responsive SVGs can sometimes have issues in IE or Edge.
- Coding the width and height takes longer than deleting it.
- If I've designed an icon at a size, I want the SVG to remember that without me having to always add code (I can always override the included size with CSS).
All that said... it would be nice for XD to give us a choice when exporting (like Illustrator does). That's a good feature request, which you can make at https://adobexd.uservoice.com/ If such a feature request already exists, upvote it to add your voice, otherwise you can make a new feature request.