How to eliminate custom posts where the “date” value is expired?

You can’t use date() with no parameters. See http://php.net/manual/en/function.date.php.

Try this for your meta_query argument:

'meta_query' => array(
    array(
        'key' => '_gigswhen',
        'value' => time()
        'compare' => '<'
    )
)

Hata!: SQLSTATE[HY000] [1045] Access denied for user 'divattrend_liink'@'localhost' (using password: YES)