Fix the lack of LAr 2d cell occupancy plots

Pavol Strizenecrequested to merge
pavol/athena:fix_LAr2dplots into 22.0

This is to fix the absence of proper LAr 2d cell occupancy plots, which were unintentionally removed. when trigger usage was included. Therefore we will see more LAr Cell plots in the monitoring, but no other changes. Jira bug report: https://its.cern.ch/jira/browse/ATLLARSWDPQ-328

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