If I were to do just "dnf copr remove gnome-info-collect", I would get these:

 Error: use format `copr_username/copr_projectname` to reference copr project
 Error: bad copr project format

...so in theory I needed to use "dnf copr remove vstanek/gnome-info-collect"

...however, it would be nice if DNF was more helpful to the user by either realizing that there is only one COPR matching this name on my system even if I don't specify the author's name (and asking if that's the one I want to delete), or listing potential matches with a "Did you mean one of these repositories?" kind of message...