Outdated "Running DaVinci on the grid" due to Centos7 EOL

The section https://lhcb.github.io/starterkit-lessons/first-analysis-steps/davinci-grid.html
is not up-to-date anymore.

I expect this can be fixed following https://twiki.cern.ch/twiki/bin/viewauth/LHCb/FAQ/GangaLHCbFAQ#How_do_I_run_old_Gaudi_appli_AN1

This could may be added to #308.