If you and your sentient clone somehow agree that you murdering him is "cool", doesn't make you murdering him any less of a murder. The example is rather contrived, since an atom-by-atom clone of you would have the same memory and drives as you (it probably wouldn't even be possible to identify which is the clone), so it would seem in this scenario you both appear to have a death wish. But acting on somebody else's death wish and murdering them does not make it "not murder" just because they expressed a death wish.