I have installed several x-themes before choosing x-theme Agency. I built my website www.agile4all.nl using the theme Agency. I used Agency as start and changed everything i wanted. It’s my first website and it looks great, so I am very pleased with the theme. However, the most 404’s comes from built-in demo url’s, which are not in use. I took a screenshot of some of them. See image:

Google find these and others like unused tags somewhere, I can’t. So, where can i find these and can I delete them? I know i can use a 404 page or I can redirect them one by one (using Yoast), but i really like to remove them for good. Is this possible?
Thnx in advance!