For unpitched percussion instruments you may want to use the “blank clef” (the one that consists
of a bit of empty staff). Although this just makes the staff start with a gap instead of a clef, you
position the blank clef just like any other clef instead of trying to delete the clef that’s already there.
Once you have put a blank clef change somewhere, you can’t select it and delete it – there’s nothing
there to select. Instead, put a different clef on top and hit Delete.