In your browser settings under search configure a new custom search with the following string:
https://www.google.com/search?q=%25s&udm=14
That attaches the string udm=14 to every search in the browser toolbar, which omits all AI features.
The downside is that if you're searching for translation or currency conversion it won't show you those as google features on top of the search results either, but only as separate links.
Nope, you can't disable it at all, this is the only workaround that currently gets rid of their crap.