L1CaloFEX[ToolInterfaces]: cmake and package cleanups

L1CaloFEX:

• remove atlas_depends_on_subdirs
• enable flake8 and fix code
• fixes to component declaration

L1CaloFEXToolInterfaces:

• cmake fix for interface library

Trigger/TrigT1/L1CaloFEX/L1CaloFEXSim/python/eFEXDriverConfig.py

-from L1CaloFEXSim.L1CaloFEXSimConf import LVL1__eFEXSim
+# Copyright (C) 2002-2020 CERN for the benefit of the ATLAS collaboration
+from L1CaloFEXSim.L1CaloFEXSimConf import LVL1__eFEXDriver
 
 class Run3eFEXDriver (LVL1__eFEXDriver):
     __slots__ = []