Remove checksum type profile variables

Remove checksum type profile variables

Remove support for the krb5.conf relations ap_req_checksum_type,
kdc_req_checksum_type, and safe_checksum_type.  These values were
useful for interoperating with very old KDCs, which should no longer
be deployed.

Additionally, kdc_req_checksum_type was incorrectly documented as only
applying to single-DES keys; in practice it also worked for RC4.  The
other two were not clearly documented, but safe_checksum_type did
allow use of hmac-md5-rc4 for any enctype, and ap_req_checksum_type
did not impose any limitations.

[ghudson@mit.edu: edited commit message]

ticket: 8804 (new)