AnalysisTop: 21.2 update METsyst calibration
Add advanced user configurable option to define the path to previous METsyst calibration files
Removed call to AFII specific METsyst config file if using latest July2020 recommendations (AFII now to use FS recommendations as described here: https://twiki.cern.ch/twiki/bin/viewauth/AtlasProtected/EtmissRecommendationsFullRun2#Configuration_File)
Edited by Jonathan Jamieson