Remove (now detrimental) debug line

Not intended to laugh at the user, I promise ;_; Was running into a bug
due to too much usage of empty() to coerce variables into booleans.

plugin/topic_mute/src/Subs-TopicMute.php

@@ -25,7 +25,6 @@ function topic_is_muted($topic, $user = -1)
 {
     global $context, $smcFunc, $user_info;
     if ($user_info['is_guest']) {
-        die('lol');
         return false;
     }