Spell out duplicate hook locations.

props DrewAPicture.
fixes #25658.

Built from https://develop.svn.wordpress.org/trunk@25868


git-svn-id: http://core.svn.wordpress.org/trunk@25868 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-admin/admin-post.php

@@ -23,7 +23,7 @@ require_once(ABSPATH . 'wp-admin/includes/admin.php');
 
 nocache_headers();
 
-//duplicate_hook
+/** This action is documented in wp-admin/admin.php */
 do_action( 'admin_init' );
 
 $action = 'admin_post';