Removed throat data from VTK file.

The data are still there, but we don't want to visualize them, because
the VTK file can show only Np items. (it has been designed for pores).
We can visualize throats by adding some methods inside VTK file for
throat coordinates and connection. Even after that, I'm  not still sure
that we can show both pore and throat data on one VTK file .
But in the meantime, since they do not represent correct values, we
should remove them from final visualization.