Looks like you can set browser.urlbar.suggest.quicksuggest.sponsored to false to remove sponsored suggestions. Searching about:config for "sponsor" brings up a few items.
The point being made by the OP and the comments here is that shouldn't be necessary. When every update includes new obnoxious shit that you don't want and have to figure out how to revert, it's no longer an improvement. Fighting the software you use is a horrible position to be in.
