move mcweighter from Susy3LepCutflow  to SusyNtAna
drop SusyNtAna::getEventWeight and related functions

By now people should really be using MCWeighter. Having these
functions defined in multiple places is very confusing and
bug-prone. Details: delete
- SusyNtAna::getEventWeight()
- SusyNtAna::m_sumwMap
- SusyNtTools::getEventWeight
- SusyNtTools::getSumw
- SusyNtTools::getCrossSection
- SusyNtTools::getXsecTimesEff(
- SusyNtTools::getPileupWeight