Remove hits in third time bin variable for xAOD::StripCluster

It looks like this variable has never been used in the past. We can always add it back should we need it in the future

/cc @ncalace @lgagnon

Event/xAOD/xAODInDetMeasurement/Root/StripClusterAuxContainer_v1.cxx

@@ -13,6 +13,5 @@ namespace xAOD {
         AUX_VARIABLE(globalPosition);
         AUX_VARIABLE(rdoList);
         AUX_VARIABLE(channelsInPhi);
-        AUX_VARIABLE(hitsInThirdTimeBin);
     }
 }