Switch to current_theme_supports(menus) internally. Adding theme support for...

Switch to current_theme_supports(menus) internally. Adding theme support for 'nav-menus' is deprecated in favor of register_nav_menu(s). fixes #13825.

git-svn-id: https://core.svn.wordpress.org/trunk@15193 1a063a9b-81f0-0310-95a4-ce76da25c4cd