RFR: 8316295: Serial: Remove empty Generation::promotion_failure_occurred

[Albert Mingkun Yang]

Trivial removing redundant code.

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Commit messages:
 - s1-promo-fail

Changes: https://git.openjdk.org/jdk/pull/15744/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15744&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316295
  Stats: 8 lines in 2 files changed: 0 ins; 8 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15744.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15744/head:pull/15744

PR: https://git.openjdk.org/jdk/pull/15744