Remove translation of single placeholder can't be translated

Follow up of https://www.drupal.org/node/2854444#comment-12079444, subcomment 3

+++ b/src/Plugin/Field/FieldWidget/ParagraphsWidget.php
@@ -279,11 +279,7 @@ class ParagraphsWidget extends WidgetBase {
+        $info['validation_error'] = $this->createMessage($this->t('@messages', ['@messages' => strip_tags(implode('\n', $messages))]));

Quote from @berdir: "to answer your question. Yes, validation messages are translated already. But this doesn't actually translate anything anyway. It just passes everything through a single placeholder, that can't be translated. But as I said, lets do a separate issue to clean this up."

So we need to remove that t() call for this case because its not needed.