GeoModelInterfaces+LArElecCalib: more cmake fixes

Frank Winklmeierrequested to merge
fwinkl/athena:cmake_LArElecCalib into master

Fix cmake warning introduced by !31813 (merged). atlas_install_headers is not needed if an interface library already installs the headers. Also did some general cmake cleanups:

  • Remove deprecated atlas_depends_on_subdirs
  • Declare files belonging to interface libraries
  • Tidy up library dependencies (CxxUtils was missing, ROOT not needed)

cc @akraszna @ssnyder

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