[test][1pni] Add a test in 1d and remove the one in 2d
There are enough other ni convection tests in 1d and there's the 1pni conduction test in 2d. mpfa test was removed because it doesn't work in 1d but there is also still another one there.
There are enough other ni convection tests in 1d and there's the 1pni conduction test in 2d. mpfa test was removed because it doesn't work in 1d but there is also still another one there.