RFR: 8274656: Remove default_checksum and safe_checksum_type from krb5.conf

[Weijun Wang]

Remove support for the 2 settings. Remove classes around the KRB_PRIV and KRB_SAFE message types that were never used in Java.

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Commit messages:
 - 8274656: Remove default_checksum and safe_checksum_type from krb5.conf

Changes: https://git.openjdk.java.net/jdk/pull/5788/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5788&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8274656
  Stats: 1345 lines in 13 files changed: 0 ins; 1343 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5788.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5788/head:pull/5788

PR: https://git.openjdk.java.net/jdk/pull/5788