migrate PileUpEventInfo to xAOD::EvenInfo

Merged Marcin Jerzy Nowak requested to merge mnowak/athena:PileUpEventInfo.migration into master

Migrated PileUpEventInfo to xAOD::EvenInfo

Jira: https://its.cern.ch/jira/browse/ATLASSIM-2633

Edited by Marcin Jerzy Nowak

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