RFR: 8337192: [BACKOUT] JDK-8336098 G1: Refactor G1RebuildRSAndScrubTask

[Albert Mingkun Yang]

Clean revert of JDK-8336098.

Test: 4/100 failing rate before  and 0/400 afterwards

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Commit messages:
 - revert

Changes: https://git.openjdk.org/jdk/pull/20324/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20324&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8337192
  Stats: 116 lines in 1 file changed: 64 ins; 19 del; 33 mod
  Patch: https://git.openjdk.org/jdk/pull/20324.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20324/head:pull/20324

PR: https://git.openjdk.org/jdk/pull/20324