message: Use renamed unused param macro
diff: using namespace std;
  using namespace axom::multimat;
  -MultiMat::MultiMat(DataLayout AXOM_NOT_USED(d), SparsityLayout AXOM_NOT_USED(s))
  +MultiMat::MultiMat(DataLayout AXOM_UNUSED_PARAM(d),
  + SparsityLayout AXOM_UNUSED_PARAM(s))
  : m_ncells(0)
  , m_nmats(0)
  , m_cellMatRel(nullptr)
  