Make dunepythontest work again

The recent "Hey let's change this, just because I don't like it"(TM)-change
in ParameterTree broke the test. While the whole interface says that values
and subtrees are different things we now pretend that they are the same
making this code throw an exception.

dune/fufem/test/dunepythontest.cc

@@ -529,7 +529,6 @@ int main(int argc, char** argv)
             << std::endl << "tree = {}"
             << std::endl
             << std::endl << "tree[1] = 'one'"
-            << std::endl << "tree['1.0.0'] = 'one'"
             << std::endl << "tree['two'] = 2e-0"
             << std::endl << "tree['3'] = {}"
             << std::endl << "tree['3']['a'] = 'aaa'"