I had the same issue for one of my wordpress installs.
I solved it by updating wp_postmeta table like this:
UPDATE wp_postmeta SET meta_value = REPLACE(meta_value,'/your/local/path/','')
and then running regenerate-thumbnails plugin, so that _wp_attachment_metadata is updated as well (it should become corrupted in step 1, because when php serializes a string, it stores string length, which now has changed).
It’s pretty easy- just open addthis_social_widget.php file, go to line 110 (if you’re using the newest version of this plugin) and change the line which reads:
if (is_feed()) return $content;
to
if (is_feed() || is_page()) return $content;
Voila, your static pages don’t have this widget anymore.
