How to delete a folder (or file) that's "in use"

I've got a folder from Adobe Illustrator CC 2018 that won't delete, and I can't figure out what's blocking it.

It is one empty folder (ro.lproj) deep in an application package.

lsof doesn't seem to reveal anything holding the folder open, but maybe I'm not using it correctly.

I've rebooted several times over several weeks.

rm -f hasn't succeeded either.

Where should I look next?