Almaz is right – “There is an option that allows you to rename or hide this link. It is located here: Gallery > Gallery Settings > NextGEN Basic Thumbnails > Show slideshow link / Slideshow link text”
But in my NextGen v 2.0.30 I say “No” in “Show slideshow link” and also say “No” in “Show piclens link” (it shows “Show slideshow” in russian language: “Смотреть слайдшоу”)