$text=preg_replace('|<div class="menu" onclick="location.href='/ex/catalog/5/">(.*?)<div class="navi">|is', '', $text);
Добавлено 12.06.16 в 21:57:16:
или же $text=str_replace('|<div class="menu" onclick="location.href='/ex/catalog/5/"><div class="navi">|is', '', $text);