SubgridXYFunctionalAssemblerTest broken for ALUGrid in 3d

This suggests strongly that there is an issue with the SubgridL2FunctionalAssembler or the way it is tested.

The test for SubgridH1FunctionalAssembler fails for ALUGrid<3, 3, simplex, nonconforming> but this might relate to issues with ALUGrid that exist by the time of this writing.