Yeah, thanks. I found that myself, but somehow this particular comp isn't removed by the "Remove unused footage" command. Is there any way to see where it might be used?
What Todd said below.
Compositions are not footage items in the sense that is relevant for the Remove Unused Footage command.
There are several commands described in the page that I linked to, for different types of cleanup and consolidation.
I was hoping that you'd read this paragraph:
"To remove unselected compositions and unused footage items from selected compositions in the Project panel, choose File > Reduce Project."
Try selecting the compositions that you want to keep and using the Reduce Project command. Be sure to make a backup first, in case this doesn't work as you intend.