Bug 1701804 - Do not send hostname in EHLO command in SmtpClient.jsm. r=mkmelin

From rfc5321#section-2.3.5

> A domain name that is not in FQDN form is no more than a local alias.
> Local aliases MUST NOT appear in any SMTP transaction.

--HG--
extra : rebase_source : ecaebe98acc678c754589619592c9a3c6e5620b2

mailnews/compose/src/SmtpClient.jsm

@@ -738,11 +738,6 @@ class SmtpClient {
       return helloArgument;
     }
 
-    try {
-      return Cc["@mozilla.org/network/dns-service"].getService(Ci.nsIDNSService)
-        .myHostName;
-    } catch (e) {}
-
     try {
       // The address format follows rfc5321#section-4.1.3.
       let netAddr = this.socket?.transport.getScriptableSelfAddr();