Revert "Merge branch 'enable-public-headers-builds' into 'master'"

After enabling the test build of public headers I found that we have many DetDesc specific public headers that are implicitly never used when building in DD4hep mode, but that means that trying to build them stand alone cannot work.

Fixing the compilation of all public headers in these conditions takes too much time, so for the time being I'm turning it off.

/cc @rmatev

This reverts merge request !984 (merged)