I'm confused... Normally, an unsubscribe link simply takes the email address that was sent to it, handles saving the data to the database and displays a message that says "You have been removed from our mailing list!". You do not want the user to have to retype the email address in and submit another form. That would just be annoying to the user.
It that script, just GET the email address (you already have that and it was inside of the unsubscribe link on the original email that the user clicked on), open your database, delete their info or if you want to keep their data for future use, just make it not-mailable so no further emails will be sent. Lastly, echo back a small page with your company's header/footer and a simple "You have been removed, etc" message in the middle. (No links or menu buttons needed as they don't want to be there.)
Did that make sense? Hope so, Good luck...