Remove deprecated `oldFile` helper for 1.4

[carbontwelve]

if (! function_exists('oldFile')) {
    /**
     * @deprecated
     * @throws Exception
     * @todo remove from version 1.4 onwards
     */
    function oldFile() {
        throw new Exception('The oldFile function has been deprecated in favour of using rememberedFile');
    }
}

https://github.com/photogabble/laravel-remember-uploads/blob/master/src/helpers.php#L33-L42