Turn EM Tower & Cluster building off, no clients left

Looking at the data-flow in standard reconstruction, I realized that the EM-Towers and furthermore EM-Clusters lost their purpose (client). The only client was the AOD cell-writing. With this MR, the flag CaloRecFlags.doEmCluster is false by default, so the Algorithms

CaloTowerAlgorithm/EmTowerBldr CaloClusterMaker/LArClusterMaker CaloClusterMaker/LAr7_11NocorrClusterMaker LArDigitThinnerFromEMClust/LArDigitThinnerFromEMClust

are no longer scheduled and the following collections no longer written to the ESD: LArClusterEM7_11Nocorr LArClusterEM LArDigitContainer_EMClust

The only visible difference in the AOD is fewer cells in the AODCellContainer. Cells belonging to egammaClusters, MuonClusterCollection or InDetTrackParticlesAssociatedClusters are still written to the AOD. That makes the AOD some 50kBytes/event smaller, which AMSG3 will certainly appreciate. This has an impact on a possible re-calibration of egamma in AODFix. If these cells are really necessary in the AOD, we should find a more straightforward way of adding them instead of the over-complicated sequence of Algs and Tools that I am removing here.