Should I just delete it, or is it better to close as a duplicate?
Thanks for bringing this up on meta so quickly. As already remarked by @Tetsujin in the comments:
We can keep it & link it as a duplicate - which gives Google a greater chance of finding the answer in future. I'll vote to close as a dupe; it doesn't reflect on the quality of the question, merely links it to an existing one with a highly-voted answer.