RFR: 8279018: CRC calculation in CDS should not include _version and _head_size

[Yumin Qi]

Please review the simple change for not including _version and _header_size in crc computation. These two fields are checked separately and they should not affect crc.

tests: tier1,tier4

Thanks
Yumin

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Commit messages:
 - 8279018: CRC calculation in CDS should not include _version and _head_size

Changes: https://git.openjdk.java.net/jdk/pull/6899/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=6899&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8279018
  Stats: 2 lines in 1 file changed: 1 ins; 1 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/6899.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/6899/head:pull/6899

PR: https://git.openjdk.java.net/jdk/pull/6899