Revert "Fixed PHP notice on other admin pages. (#1)" (#2)

This reverts commit 6d06869.

Upstream PR remains: woocommerce#72

Author: sun

includes/class-wc-amazon-payments-advanced-order-admin.php

@@ -167,9 +167,6 @@ public function meta_box() {
 	public function authorization_box() {
 		global $post, $wpdb, $theorder;
 
-		if ( empty( $post->ID ) ) {
-			return;
-		}
 		$actions  = array();
 		$order_id = absint( $post->ID );