Also tried replacing the page-builder.js, using FileZilla.
This was my first time using it or changing theme files at all, so I’m not certain it worked. (FileZilla gave me conflicting messages about whether the transfer had worked. The log at the top seemed to say it had failed, but the file appeared in the ‘Successful transfers’ tab at the bottom. Also, the new file itself, showing in the .js folder, was shown as having ‘0 bytes’, rather than the ~140 bytes I guess it actually should have.)
Anyway, clear browser cache, logged out, restarted browser, logged in to WP admin: Swift PageBuilder is not there 🙁