Hi!
That looks like something your theme is putting in place, so ideally you’d modify the appropriate template or otherwise make a change to handle that at theme-level. Since I’m unfamiliar with your theme I can’t help with that, I’m afraid, but perhaps you could put an extra CSS rule in place to hide it?
article > a > div.entry-thumbnail:first-child { display: none }
If you only wanted this to take effect on list view you could further refine the above to:
.events-list article > a > div.entry-thumbnail:first-child { display: none }
Does that help?