In wp_trash_post(), rename the trash_post action to wp_trash_post to avoid...

In wp_trash_post(), rename the trash_post action to wp_trash_post to avoid collision with the wp_transition_post_status() trash_post state transition. Props SergeyBiryukov. fixes #15628

git-svn-id: https://core.svn.wordpress.org/trunk@18974 1a063a9b-81f0-0310-95a4-ce76da25c4cd