prevent (or support) slicing for 3D crystals

Replace code

    if (iff && re_layout.numberOfSlices() > 1 && !iff->supportsMultilayer())
        throw std::runtime_error("LayoutStrategyBuilder::checkInterference: "
                                 "interference function does not support multiple layers");

that has been removed in 6bb163ab "ProcessedLayouts: rm m_n_slices"