Re-enable test_loop_cutting.py::test_staggered_iteration

It passes on current master, so don't xfail it.

pystencils_tests/test_loop_cutting.py

@@ -29,10 +29,6 @@ def offsets_in_plane(normal_plane, offset_int, dimension):
     return result
 
 
-# TODO this fails because the condition of the Conditional is not simplified anymore:
-# TODO: ---> transformation.simplify_conditionals
-# TODO this should be fixed
-@pytest.mark.xfail
 def test_staggered_iteration():
     dim = 2
     f_arr = np.arange(5**dim).reshape([5]*dim).astype(np.float64)