RFR: 8297639: Remove preventive GCs in G1

[Thomas Schatzl]

Hi all,

  can I have reviews for this removal of preventive gcs for G1?

This feature seems to bring more harm than benefit, so after disabling it by default in JDK 20 (reasons described in [JDK-8293861](https://bugs.openjdk.org/browse/)), this change removes the feature altogether.

This is almost a backout of the original change.

Testing: tier1-5

Thanks,
  Thomas

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Commit messages:
 - Remove preventive gc

Changes: https://git.openjdk.org/jdk/pull/11654/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11654&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297639
  Stats: 185 lines in 16 files changed: 6 ins; 159 del; 20 mod
  Patch: https://git.openjdk.org/jdk/pull/11654.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11654/head:pull/11654

PR: https://git.openjdk.org/jdk/pull/11654