wp_wc_set_checkout_fields_value.php

<?php

// set some checkout fields to empty
add_filter('woocommerce_checkout_get_value','woo_ongkir_checkout_get_value', 10, 2);
function woo_ongkir_checkout_get_value($default, $field)
{
	$empty_fields = array(
		'billing_postcode',
		'billing_state',
		'billing_city',
		'billing_district',
		'shipping_postcode',
		'shipping_state',
		'shipping_city',
		'shipping_district'
	);

	if(in_array($field, $empty_fields)) {
		return "";
	}
	else {
		return $default;
	}
}