update xs for BSM VBFHH bbyy
update the XS numbers based on the combination formula shown today on s9 and 10 of https://indico.cern.ch/event/1416138/contributions/6020905/attachments/2886090/5058219/ABetti_HH_SignalCrossSections.pdf
calculations are in https://docs.google.com/spreadsheets/d/1kE1l5AsuKnER_vyEhQSpDJlbaLWyZHUfzERNsKFTq88/edit?gid=79066893#gid=79066893