Remove unnecessary test_email extra parameter for mailer->send

It was used only to prevent appending unprocessed subscribers into error message.
Since the message is now composed by on demand by MailerError the parameter is not needed any more.

[MAILPOET-1154]

tests/unit/Mailer/Methods/ErrorMappers/SMTPMapperTest.php

@@ -42,7 +42,7 @@ class SMTPMapperTest extends \MailPoetTest {
       . '" (code: 550)' . PHP_EOL
       . '>> RSET' . PHP_EOL
       . '<< 250 Reset OK' . PHP_EOL;
-    $error = $this->mapper->getErrorFromLog($log, 'test@example.com', []);
+    $error = $this->mapper->getErrorFromLog($log, 'test@example.com');
     expect($error->getMessage())
       ->equals('Expected response code 250/251/252 but got code "550", with message "550 No such recipient here" (code: 550)');
     expect($error->getSubscriberErrors()[0]->getEmail('moi@mrcasual.com'));