RFR: 8364756: JFR: Improve slow tests

[Erik Gahlin]

Could I have a review of a PR that improves the speed of some of the JFR tests?

Thanks
Erik

-------------

Commit messages:
 - Revert test change as it did not yield improvement
 - Initial

Changes: https://git.openjdk.org/jdk/pull/26644/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26644&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8364756
  Stats: 28 lines in 7 files changed: 8 ins; 8 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/26644.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26644/head:pull/26644

PR: https://git.openjdk.org/jdk/pull/26644