If you have FileMaker Advanced, you can use a database design report for this if you are careful. The report is buggy so you can't trust the part of the report where it lists "scripts that use this script", but you can search the report for the script's name and if you can't find any parts of the report that refer to the script except the part of the report that lists the script itself, then you can delete the script.
I was worried you'd say that ... I have an old print out of one of those reports and saw that column but hoped there would be a better way out. I think at this point it would be safer to just leave them which is unfortunate.
It's not terribly difficult to do a text search of the database design report for a script name. If it's not used anywhere, you'll get exactly 4 "hits", the "table of contents" type list of all the scripts by name, The "next script" and "previous script" tags and then the listing of that script's step itself. So it can take just a few minutes to confirm that the scritp is not used anywhere. If your script name is generic enough that it might match other objects in your database, you can temporarily rename it to something unique just before you generate the report.