RFR: 8325643: G1: Refactor G1FlushHumongousCandidateRemSets

[Albert Mingkun Yang]

Simple refactoring to ensure both paths are checked regarding remset status.

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Commit messages:
 - review
 - if-else
 - g1-eager-reclaim

Changes: https://git.openjdk.org/jdk/pull/17808/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=17808&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8325643
  Stats: 15 lines in 1 file changed: 3 ins; 1 del; 11 mod
  Patch: https://git.openjdk.org/jdk/pull/17808.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17808/head:pull/17808

PR: https://git.openjdk.org/jdk/pull/17808