I’ve messed up the admin search functionality. Help!

You can check if is_admin or not in the first line of the function

add_filter('posts_where', 'advanced_search_query' ); 
function advanced_search_query( $where )
{
    if(is_admin()){
        return $where;
    }
    if( is_search() ) {
        global $wpdb;
        $query = get_search_query();
        $query = like_escape( $query );

        // include postmeta in search
         $where .=" OR {$wpdb->posts}.ID IN (SELECT {$wpdb->postmeta}.post_id FROM {$wpdb->posts}, {$wpdb->postmeta} WHERE {$wpdb->postmeta}.meta_key = 'bible_reference' AND {$wpdb->postmeta}.meta_value LIKE '%$query%' AND {$wpdb->posts}.ID = {$wpdb->postmeta}.post_id)";

         // include taxonomy in search
        $where .=" OR {$wpdb->posts}.ID IN (SELECT {$wpdb->posts}.ID FROM {$wpdb->posts},{$wpdb->term_relationships},{$wpdb->terms} WHERE {$wpdb->posts}.ID = {$wpdb->term_relationships}.object_id AND {$wpdb->term_relationships}.term_taxonomy_id = {$wpdb->terms}.term_id AND {$wpdb->terms}.name LIKE '%$query%')";


        if(WP_DEBUG)var_dump($where);
    }
    return $where;
}