MadGraphControl: fix for gridpacks
We recently changed our handling of PDFs in MGC. Previously we would create a local directory with LHAPDF data (datasets and pdfsets.index). In more recent versions of MG this is no longer necessary and from 3.4.X on it did no longer work. So we removed the no-longer-needed workaround and rely on PDFs from cvmfs. We also no longer link the PDFs to PROC*/lib/PDFsets (previously this was done directly before event generation, both from gridpacks and on-the-fly) and indeed MG is is working fine with an empty PDFsets directory, picking up PDFs from cvmfs.
It is however not working with no PROC*/lib/PDFsets at all.
So, with this fix, we no longer omit the (empty) PDFsets directory from gridpacks. This way gridpacks also contain an (empty) PDFsets directory.
This is a bit of a workaround but easier than updating the MadGraph fortran code requiring this directory.