fix a few "unused variable" warnings that occur on more uncommon compilers

i.e. on ICC. the compiler is right in producing warnings here, though.

tests/models/test_quadrature.cpp

@@ -296,7 +296,6 @@ void testQuadrature()
 {
     std::cout << "testing SCV quadrature...\n";
 
-    std::bitset<dim> isPeriodic(false);
     std::array<int, dim> cellRes;
 
     std::fill(cellRes.begin(), cellRes.end(), 10);