ClassIDSvc: code cleanup and simplification

Some code cleanup and simplification in ClassIDSvc, i.e.:

• drop support for reading package version from clid.db
• use try_emplace to insert and check for duplicates at the same time
• remove the now unused "Internal" methods
• remove using namespace std
• consistent use of ATH_MSG macros
• replace boost::lexical_cast with std::stol
• replace use of boost::tokenize with boost::split

Also update test references and do not add testing classes to clid.db in DataModelTestData[Read,Write] packages.