Hello,
Thank you for your question regarding automatically removing forwarded emails. You can do this by creating the forwarder without creating the email account. This is not recommended since it does not allow you to send email as that user.
The best solution is to set up a filter/rule in your email client, such as Outlook, MacMail, Thunderbird, or Webmail. For example, you could create a rule to forward the email, then move to trash.
Thank you,
John-Paul