Remove e-mail field for registered users in comment form

Registered / logged in users are presented the comment form with E-Mail field to be input. When the user input a different e-mail and the moderator decides to ban the user by e-mail address... it does nothing, as the e-mail submitted is not attached to the user, so user still can keep posting messages.

Ideal is to remove the e-mail field from the form for logged in users and take always the registered e-mail address.