RFR: 8324147: Serial: Remove generation::compute_new_size

[Albert Mingkun Yang]

Trivial removing effectively dead code.

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Commit messages:
 - s1-new-size

Changes: https://git.openjdk.org/jdk/pull/17487/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17487&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8324147
  Stats: 7 lines in 3 files changed: 0 ins; 5 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/17487.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17487/head:pull/17487

PR: https://git.openjdk.org/jdk/pull/17487