To prevent the link to your WordPress domain appearing below the topic title, deselect the “Add Featured Links” option on your WP Discourse Publishing settings page. To remove the featured link from posts that have already been published, the link can either be hidden with CSS, or it can be removed from your Discourse site’s database. I am away from work for the next couple of days, but can take care of that for you when I get back to work on Wednesday.
If you can wait until Wednesday, I can give you a hand with this. If you need to do it sooner than that, you could try creating a new topic in our support category that asks how to create topics through the API from a CSV file.