security/krb5-appl: Deprecate and expire

krb5-appl has not been supported by MIT for a while. The krb5-appl
applications would still work with a kdc using a key encrypted with
an older cipher. The older ciphers have been deprecated and
subsequently removed, resulting in krb5-appl providing no function
anymore.

I am sure everyone is using ssh with GSSAPI enabled these days.