Original path: JoomlaFolder/components/com_easyblog/themes/wireframe/blogs/entry/post.cover.php
You can template override it at JoomlaFolder/templates/yourCurrentTemplate/html/com_easyblog/blogs/entry/post.cover.php and remove the "eb-image-popup-button" class on the template override post.cover.php file.
Do take note that you need to create the folders manually if you don't see it.