Hello @Brian_Fewell,
Asana created custom fields cannot be deleted.
Now in order to find where your other field might be used you can use this great tool for example: iDO Tools - Improve Asana with our tools and automations
In your case it is a bit strange as it says Asana created but then also created by you and uneditable. I think you might be right with your assumption that you duplicated the Asana custom field and that is why the text in the description was copies over as well but in your case does not apply since you created the field by duplicating.
Now since it says the field is used in a template did you check with your team? As the field was made available to your org.
If you cannot figure it out I recommend reaching out to support so they can assist with this.