Tag to be used with the 21.X branches of atlas/athena. Updates in this tag: - Updated AthAnalysisExternals to use LCG_96b; * Removed the build of Eigen, FastJet and FastJetContrib from the project as now "new enough" versions are coming from LCG_96b; - Updated all externals built by AnalysisBaseExternals to be in sync with the versions available in LCG_96b.