In miscellaneous publishing actions, use :last-child instead of a separate...

In miscellaneous publishing actions, use :last-child instead of a separate misc-pub-section-last class to control borders. Allows for sane use of the post_submitbox_misc_actions hook. (Actually uses :first-child for browser compat reasons.) fixes #19604.

git-svn-id: https://core.svn.wordpress.org/trunk@20077 1a063a9b-81f0-0310-95a4-ce76da25c4cd