RFR: 8338036: Serial: Remove Generation::update_counters

[Albert Mingkun Yang]

Trivial removing redundant code.

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Commit messages:
 - s1-perf-counter

Changes: https://git.openjdk.org/jdk/pull/20509/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20509&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8338036
  Stats: 2 lines in 1 file changed: 0 ins; 1 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20509.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20509/head:pull/20509

PR: https://git.openjdk.org/jdk/pull/20509