readme: drop unencrypted client example

We don't want to encourage people to turn TLS off.

README.md

@@ -45,40 +45,7 @@ func main() {
 }
 ```
 
-If you need more control, you can use `Client` instead. For example, if you
-want to send an email via a server without TLS or auth support, you can do
-something like this:
-
-```go
-package main
-
-import (
-	"log"
-	"strings"
-
-	"github.com/emersion/go-smtp"
-)
-
-func main() {
-	// Setup an unencrypted connection to a local mail server.
-	c, err := smtp.Dial("localhost:25")
-	if err != nil {
-		return err
-	}
-	defer c.Close()
-
-	// Set the sender and recipient, and send the email all in one step.
-	to := []string{"[email protected]"}
-	msg := strings.NewReader("To: [email protected]\r\n" +
-		"Subject: discount Gophers!\r\n" +
-		"\r\n" +
-		"This is the email body.\r\n")
-	err := c.SendMail("[email protected]", to, msg)
-	if err != nil {
-		log.Fatal(err)
-	}
-}
-```
+If you need more control, you can use `Client` instead.
 
 ### Server