In nextgen-gallery/view/gallery.php, find these lines:
<?php if ($gallery->show_slideshow) { ?>
<!-- Slideshow link -->
<div class="slideshowlink">
<a class="slideshowlink" href="<?php echo $gallery->slideshow_link ?>">
<?php echo $gallery->slideshow_link_text ?>
</a>
</div>
<?php } ?>
Either comment them out or remove them.
De-activate this in the gallery options.
Options -> Gallery -> Use slideshow (or similar, in German it’s “Slideshow verwenden:”)
This sets $gallery->show_slideshow from the above code to false.
for nextgen gallery plugin version 0.98
wp-content/plugins/nextgen-gallery/nggfunctions.php around line 236
comment
//$out .= '<div class="slideshowlink"><a class="slideshowlink" href="' . $nggRewrite->get_permalink($args) . '">'.$ngg_options['galTextGallery'].'</a></div>';
would be nice to be a configurable option in nextgen admin