Remove support for `_2` and `_3` macros
Follows staging/dune-uggrid#57 (comment 79565) from @oliver.sander about UG_USE_NEW_DIMENSION_DEFINES
macro in UGGrid.
Follows staging/dune-uggrid#57 (comment 79565) from @oliver.sander about UG_USE_NEW_DIMENSION_DEFINES
macro in UGGrid.