Yes it is obsolete for quite some time, at least form Oracle7 era... and yet they still include it in any new distribution...

catdbsyn.sql can be used if you want to have *private* synonyms for all DBA_% views, which is kind of silly since there are public synonyms for all those views. So you don't need to run this script at all. It wouldn't do you any harm (except for a bounch of useless objects in the catalog), but it wouldn't do you any good either.