RFR: 8369809: G1: Merge G1CollectedHeap::do_collection_pause_at_safepoint[_helper]

[Thomas Schatzl]

Hi all,

  please review this trivial fix to merge `G1CollectedHeap::do_collection_pause_helper` with `do_collection_pause`. The helper method is only called there in this single place and does not add anything but two asserts.

Testing: gha, local compilation

Thanks,
  Thomas

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Commit messages:
 - 8369809

Changes: https://git.openjdk.org/jdk/pull/27790/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27790&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8369809
  Stats: 15 lines in 2 files changed: 3 ins; 11 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/27790.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27790/head:pull/27790

PR: https://git.openjdk.org/jdk/pull/27790