Disable AP_REGISTER and AP_ADMINNOTE because of possible exploiting and uselessness

Any authenticated client (= correct username + password) can basically write "unlimited" text to the files "regform.txt" and "admnote.txt" in the blakserv directory by using AP_REGISTER or AP_ADMINNOTE messages.

This feature is not used by the current client and has security issues, someone might try to "DoS" the server harddisk with lots and big writes until it is full or fails.

This change does not fully remove the messages from the protocol, but instead disable their processing on the server-side.