RFR: 8318489: Remove unused alignment_unit and alignment_offset

[Albert Mingkun Yang]

Trivial removing dead code.

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Commit messages:
 - trivial

Changes: https://git.openjdk.org/jdk/pull/16263/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16263&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8318489
  Stats: 24 lines in 4 files changed: 0 ins; 24 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/16263.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16263/head:pull/16263

PR: https://git.openjdk.org/jdk/pull/16263