Review QFontDatabase::WritingSystem and a script that claims to generate it

qtbase/util/unicode/writingSystems.sh claims that

This script generates the QFontDatabase::WritingSystem enum.

However, when run, it produces a much longer list of writing systems than I find in qtbase/src/gui/text/qfontdatabase.h, whose history makes no mention of any Unicode Character Database updates, so I'm left suspecting the script is an archaism that we should delete; but perhaps we need to revive it and update our font database.