cmake: feature_summary printout

Using Gaudi master with athena, we are now getting the rather verbose feature_summary printout from Gaudi:

http://atlas-computing.web.cern.ch/atlas-computing/links/distDirectory/gitwww/experimentalWebArea/ardoc_web_areamastermasterGAUDI64BC7G8AthenaDbg/ARDOC_Log_2021-05-19T2101/ardoc_cmake_config.html

-- The following OPTIONAL packages have been found:

 * CppUnit
 * libunwind
 * boost_system (required version == 1.75.0)
[...]
-- The following REQUIRED packages have been found:

 * LCG (required version == 100)
 * AthenaExternals
 * Boost (required version >= 1.70)
[...]
-- Found Gaudi: /build/atnight/localbuilds/nightlies/Athena/master--masterGAUDI/build/install/AthenaExternals/22.0.35/InstallArea/x86_64-centos7-gcc8-dbg/lib/cmake/Gaudi (found version 35.3)

This is not very useful information when Gaudi is embedded in a larger project. Can we either remove this or make the printout configurable?