We just ran across this issue in this question. The problem is the plugin checks for options using the question ID, so it adds an option for every question on your site. I've submitted an issue on the Github repo so hopefully q2amarket will fix it soon.
If you are no longer using the plugin, you can delete those options. These 2 queries will do it:
DELETE FROM `qa_options` WHERE title LIKE '%_enable_adverts';
DELETE FROM `qa_options` WHERE title LIKE '%_advert_image_url';
However, if you are still using it they will come back as soon as a question is viewed. In that case, I think it can be fixed by changing line 104 in qa-adverts-layer.php to this:
$template = $this->template;
Then delete the options as above. Make sure to backup first, and make a note of which ads you added yourself as they would be deleted with that query as well.