Fix config scripts (again)

The previous fix did not work for macosx 11.3. Somehow on this system the old FindGEANT3.cmake file was used. Probably this is not a problem with the macosx version but with the usage of a case insensitive file system. To avoid the problem remove the old and obsolete file. Also do some fixes to properly initialise some cmake variables. refs #2088

changed milestone to %APR21

added BugFix Framework labels

Dear @f.uhlig, @v.friese, @p.-a.loizeau,

you have been identified as code owner of at least one file which was changed with this merge request.

Please check the changes and approve them or request changes.

added CodeOwners label

merged