Reconstruction/egamma: cmake cleanup

Cleanup the cmake configuration of a few egamma packages:

• remove atlas_depends_on_subdirs
• tidy library and external dependencies
• enable flake8 where relevant and make code compliant
• replace CLHEP/SystemOfUnits.h with the one from GaudiKernel

Reconstruction/egamma/EgammaPhysValMonitoring/CMakeLists.txt

-################################################################################
-# Package: EgammaPhysValMonitoring
-################################################################################
+# Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
 
 # Declare the package name:
 atlas_subdir( EgammaPhysValMonitoring )
 
-# Declare the package's dependencies:
-atlas_depends_on_subdirs( PUBLIC
-                          GaudiKernel
-                          PRIVATE
-                          Control/AthenaBaseComps
-                          Control/AthenaMonitoring
-                          Event/xAOD/xAODEgamma
-                          Event/xAOD/xAODEventInfo
-                          Event/xAOD/xAODPrimitives
-                          Event/xAOD/xAODTruth
-                          PhysicsAnalysis/MCTruthClassifier
-                          Tracking/TrkValidation/TrkValHistUtils )
-
 # External dependencies:
 find_package( CLHEP )
-find_package( ROOT COMPONENTS Core Tree MathCore Hist RIO pthread )
 
 # Component(s) in the package:
 atlas_add_component( EgammaPhysValMonitoring
                      src/*.cxx
                      src/components/*.cxx
-                     INCLUDE_DIRS ${ROOT_INCLUDE_DIRS} ${CLHEP_INCLUDE_DIRS}
-                     LINK_LIBRARIES ${ROOT_LIBRARIES} ${CLHEP_LIBRARIES} GaudiKernel AthenaBaseComps AthenaMonitoringLib xAODEgamma xAODEventInfo xAODPrimitives xAODTruth MCTruthClassifierLib TrkValHistUtils )
-
+                     INCLUDE_DIRS ${CLHEP_INCLUDE_DIRS}
+                     LINK_LIBRARIES ${CLHEP_LIBRARIES} GaudiKernel AthenaBaseComps AthenaMonitoringLib StoreGateLib xAODEgamma xAODEventInfo xAODPrimitives xAODTruth MCTruthClassifierLib TrkValHistUtils )