EAP-SIM peer: Remove AT_NOTIFICATION from Notification response

EAP-SIM peer: Remove AT_NOTIFICATION from Notification response

This attribute is not supposed to be used in the response frame (i.e.,
it is only in the EAP-Request/SIM-Notification frame) per RFC 4186
chapters 10.1 and 9.9. This is a minor bug since the server is required
to ignore the contents of the EAP-Response/SIM-Notification during
protected result indication per chapter 6.2.

EAP-AKA peer was already following the similar specification in RFC 4187,
but this was somehow missed in the EAP-SIM peer implementation.