I've been working on a nonfiction book revision all day. So far, all I've really done is delete text. Extra words, sentences, and paragraphs must go.
I'll know more tomorrow (and then even more over the weekend when I read the thing fresh and do another pass to make sure I've covered everything I need to cover). But I'm actually thinking that in this case, the paring of the manuscript may in fact be the revision.
I say deleting counts.