Displays a `noindex` meta tag if required by the blog configuration.

If a blog is marked as not being public then the `noindex` meta tag will be
output to tell web robots not to index the page content.

Typical usage is as a {@see ‘wp_head’} callback:

add_action( ‘wp_head’, ‘noindex’ );

function noindex() {
	_deprecated_function( __FUNCTION__, '5.7.0', 'wp_robots_noindex()' );

	// If the blog is not public, tell robots to go away.
	if ( '0' == get_option( 'blog_public' ) ) {
		wp_no_robots();
	}
}