I only know 2 addons so far using this library so far and these are
FCOItemSaver
Circonians FilterIt
Both latest versions got the text still commented.
So either another of your 300 addons is using this library and chanegd the comment line or you changed it by yourself
You can use the windows search inside the addons folder to search for "libCustomMenu" and you'll quickly find all of the addons that are using it.