Clean up code, remove unused methods.

app/Mail/UndoEmailChangeMail.php

@@ -63,7 +63,7 @@ class UndoEmailChangeMail extends Mailable
      *
      * @return $this
      */
-    public function build()
+    public function build(): self
     {
         return $this->view('emails.undo-email-change-html')->text('emails.undo-email-change-text')
                     ->subject('Your Firefly III email address has changed');