Cron: Fix a case where a cache inconsistency can cause wp_clear_scheduled_hook() to enter an infinite loop. This unravels the function from using other cron api functions to looping over the cron array directly. See #25773


git-svn-id: https://develop.svn.wordpress.org/trunk@26782 602fd350-edb4-49c9-b593-d223f7449a82