RFR: 8357306: G1: Remove _gc_succeeded from VM_G1CollectForAllocation because it is always true

[Thomas Schatzl]

Hi all,

  please review this refactoring of G1 VM GC operations to remove the _gc_succeeded members because they are not necessary any more - GC operations themselves (i.e. the doit() part) always succeed.

Testing: tier1-3, gha

Thanks,
  Thomas

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Commit messages:
 - * remove comment
 - * fix try-concurrent-...
 - * some minor refactoring
 - 8357306

Changes: https://git.openjdk.org/jdk/pull/25320/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25320&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357306
  Stats: 57 lines in 4 files changed: 2 ins; 24 del; 31 mod
  Patch: https://git.openjdk.org/jdk/pull/25320.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25320/head:pull/25320

PR: https://git.openjdk.org/jdk/pull/25320