Delete obsolete External/Herwigpp package

External/Herwigpp/CMakeLists.txt

-#
-# Package installing files from the Herwig++ generator into the offline
-# release.
-#
-
-# The name of the package:
-atlas_subdir( Herwigpp )
-
-# In release recompilation mode stop here:
-if( ATLAS_RELEASE_MODE )
-   return()
-endif()
-
-# Find the Herwig++ package. Note that LCG now calls the 7.0.1
-# version "herwig3".
-find_package( Herwig3 )
-
-# Make sure that it was found:
-if( NOT HERWIG3_FOUND )
-   message( WARNING "Couldn't find the Herwig3 package" )
-   return()
-endif()
-
-# Install files from the package:
-set( herwig_datadir "${HERWIG3_LCGROOT}/share/Herwig" )
-if( NOT IS_DIRECTORY ${herwig_datadir} )
-   message( WARNING "Can't access directory ${herwig_datadir}" )
-   return()
-endif()
-atlas_install_generic( ${herwig_datadir}/*.rpo ${herwig_datadir}/*.in
-   ${herwig_datadir}/MSSM.model
-   DESTINATION share
-   TYPENAME HerwigData )