Remove pile-up from electron plots in CampaignsARTTests
Those plots are not produced any more following !67046 (merged)
Solves warning observed in ART tests https://atlas-art-data.web.cern.ch/atlas-art-data/grid-output/main/Athena/x86_64-centos7-gcc11-opt/2023-11-20T2101/CampaignsARTTests/test_digi_reco_ttbar_mu1_inTimeTruth/dcube_wrt_last_nightly/