RFR: 8329775: Serial: Remove unused declarations in serialFullGC.hpp [v2]

[Albert Mingkun Yang]

> Trivial removing dead code.

Albert Mingkun Yang has updated the pull request with a new target base due to a merge or a rebase. The pull request now contains one commit:

  trivial

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Changes: https://git.openjdk.org/jdk/pull/18655/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18655&range=01
  Stats: 10 lines in 1 file changed: 0 ins; 10 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/18655.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18655/head:pull/18655

PR: https://git.openjdk.org/jdk/pull/18655