Hi,
Are you seeing the script in view source ? If so it is being added via code.
If you don't see it in view source, search in the javascript files being included, the file might be getting added from a js file. you need to check all the 3rd party javascript files, one of them may be adding that if the page is 404.
In chrome we can search within static files by going to "Sources" tab

Hope this helps!