Hi,

Unfortunately, this is not possible with out of the box configuration.
You can fix this with some custom CSS in the portal rebranding:

We have the following live in our instance, under "Custom Stylesheet”:

fieldset.default_requester {
   display: none !important;
}

#ticket-field-52000061188 {
   display: none !important;
}

.requester-email
{
    display: none !important; 
}