Hi, I don’t know if you’ve solved your problem but I managed to find out how to remove it. Here is the fix in case anyone else has the same problem.
in wordpress-popular-posts.php
REPLACE THIS
$post_content = ": <span class=\"wpp-excerpt\">" . $this->get_summary($wppost->ID, $instance) . "...</span>";
WITH THIS
$post_content = " <span class=\"wpp-excerpt\">" . $this->get_summary($wppost->ID, $instance) . "...</span>";