WooCommerce Postcode Address Validation 2.11.3

* Misc - Add notice for upcoming retirement of SmartyStreets integration

* Fix - Replace deprecated `is_ajax()` function calls with `wp_doing_ajax()`
* Misc - Require WooCommerce 3.9.4 or newer

* Fix - Correct a problem with Loqate, where changing the country field would not change the country being searched until a page refresh
* Misc - Remove support to legacy woo-include functions