Removes the custom_logo theme-mod when the site_logo option gets deleted.

function _delete_custom_logo_on_remove_site_logo() {
	global $_ignore_site_logo_changes;

	// Prevent _delete_site_logo_on_remove_custom_logo and
	// _delete_site_logo_on_remove_theme_mods from firing and causing an
	// infinite loop.
	$_ignore_site_logo_changes = true;

	// Remove the custom logo.
	remove_theme_mod( 'custom_logo' );

	$_ignore_site_logo_changes = false;
}