Remove Mailer struct

tests/transport_stub.rs

@@ -2,13 +2,11 @@ extern crate lettre;
 
 use lettre::transport::stub::StubEmailTransport;
 use lettre::transport::EmailTransport;
-use lettre::mailer::Mailer;
 use lettre::email::EmailBuilder;
 
 #[test]
 fn stub_transport() {
-    let sender = StubEmailTransport;
-    let mut mailer = Mailer::new(sender);
+    let mut sender = StubEmailTransport;
     let email = EmailBuilder::new()
                     .to("root@localhost")
                     .from("user@localhost")
@@ -16,6 +14,6 @@ fn stub_transport() {
                     .subject("Hello")
                     .build()
                     .unwrap();
-    let result = mailer.send(email);
+    let result = sender.send(email);
     assert!(result.is_ok());
 }