RFR: 8327130: Serial: Remove Generation::record_spaces_top

[Albert Mingkun Yang]

Trivial removing effectively dead code in the super class.

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Commit messages:
 - trivial

Changes: https://git.openjdk.org/jdk/pull/18082/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18082&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8327130
  Stats: 5 lines in 3 files changed: 0 ins; 3 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/18082.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18082/head:pull/18082

PR: https://git.openjdk.org/jdk/pull/18082