RFR: 8293623: Simplify G1ConcurrentRefineThreadControl [v2]

[Lei Zaakjyu]

> 8293623: Simplify G1ConcurrentRefineThreadControl

Lei Zaakjyu has updated the pull request incrementally with one additional commit since the last revision:

  use 'mtGC' flag

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Changes:
  - all: https://git.openjdk.org/jdk/pull/17077/files
  - new: https://git.openjdk.org/jdk/pull/17077/files/d8a338ef..42d3f53d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=17077&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=17077&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/17077.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/17077/head:pull/17077

PR: https://git.openjdk.org/jdk/pull/17077