MailTransportTest: remove reply-to addressing testing
MailTransportTest: remove reply-to addressing testing

As noted in 2380, the addressing tests do not belong in the mail transport tests and as the `ReplyToGetSetClearTest` now covers this extensively, the assertions can be removed from the `MailTransportTest`.

PHPMailer/PHPMailer,nawawi/PHPMailer,nawawi/PHPMailer,jimjag/PHPMailer,jimjag/PHPMailer,PHPMailer/PHPMailer