Avoid calling deprecated methods

This silences several compiler warnings from gcc 6.2.0 looking like this:

    dune/grid/common/grid.hh:730:45: warning:
    ‘int Dune::OneDGrid::overlapSize(int, int) const’ is deprecated:
    "overlapSize() is deprecated. Use the method on the
    LevelGridView instead." [-Wdeprecated-declarations]

See merge request !107