How to get rid of obsolete Flag Ship design?

Whenever I play GC4 Supernova I see this Flag Ship design show up in my ship yards, but it's not build-able and I can't select it and use the button to obsolete it.

I participated in the beta for GC4 on Epic over a year ago, and at some point players were able to design and build their own flag ships, so I'm pretty sure I did that. Since the original version on Epic and Supernova on Steam both use the same My Games\GalCiv4 folder, I might be seeing some leftover file there.

But I've gone through every folder in my GalCiv4 folder and cleaned out everything except a few custom races I made. So I'm wondering where this ship design is hiding and how I can get rid of it.

Any help appreciated.