RFR: 8339020: Remove unused HeapShared::calculate_oopmap

[Matias Saavedra Silva]

After JDK-8251330, `HeapShared::calculate_oopmap` is totally unused so this patch removes the method. Verified with tier1-4 tests.

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Commit messages:
 - 8339020: Remove unused HeapShared::calculate_oopmap

Changes: https://git.openjdk.org/jdk/pull/20753/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20753&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8339020
  Stats: 27 lines in 2 files changed: 0 ins; 27 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/20753.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20753/head:pull/20753

PR: https://git.openjdk.org/jdk/pull/20753