How to remove "FILE NAME SUGGESTION" from rendered HTML
I found the reason why "FILE NAME SUGGESTION" was still output.
It is because a following code still remained in template.php in Zen(not sub theme).

$GLOBALS['conf']['theme_debug'] = TRUE;


I didn't coded it by myself. So, I guess the code was added when I install some module(probably Theme developer?).

Anyways, when I comment out it,  "FILE NAME SUGGESTION" disappered.