dns: fqdn only needs domain string

This is from the caas days, when we had hyphenated subdomains flag

src/dns.js

@@ -59,22 +59,22 @@ function api(provider) {
     }
 }
 
-function fqdn(subdomain, domainObject) {
+function fqdn(subdomain, domain) {
     assert.strictEqual(typeof subdomain, 'string');
-    assert.strictEqual(typeof domainObject, 'object');
+    assert.strictEqual(typeof domain, 'string');
 
-    return subdomain + (subdomain ? '.' : '') + domainObject.domain;
+    return subdomain + (subdomain ? '.' : '') + domain;
 }
 
 // Hostname validation comes from RFC 1123 (section 2.1)
 // Domain name validation comes from RFC 2181 (Name syntax)
 // https://en.wikipedia.org/wiki/Hostname#Restrictions_on_valid_host_names
 // We are validating the validity of the location-fqdn as host name (and not dns name)
-function validateHostname(subdomain, domainObject) {
+function validateHostname(subdomain, domain) {
     assert.strictEqual(typeof subdomain, 'string');
-    assert.strictEqual(typeof domainObject, 'object');
+    assert.strictEqual(typeof domain, 'string');
 
-    const hostname = fqdn(subdomain, domainObject);
+    const hostname = fqdn(subdomain, domain);
 
     const RESERVED_SUBDOMAINS = [
         constants.SMTP_SUBDOMAIN,