Thanks @kmittman !
Actually I had to do the following instead (i.e. manipulate subfolder /etc/apt/sources.list.d instead)
sed -i '/developer\.download\.nvidia\.com\/compute\/cuda\/repos/d' /etc/apt/sources.list.d/*
sed -i '/developer\.download\.nvidia\.com\/compute\/machine-learning\/repos/d' /etc/apt/sources.list.d/*