Undeprecate require_if_theme_supports() for themes using it for legitimate...

Undeprecate require_if_theme_supports() for themes using it for legitimate reasons. see [20610]. props scribu, jkudish. fixes #20556.



git-svn-id: https://core.svn.wordpress.org/trunk@20642 1a063a9b-81f0-0310-95a4-ce76da25c4cd