RFR: 8365636: JFR: Minor cleanup

[Erik Gahlin]

Could I have review of Pr That cleans up various stuff (unnecessary imports, typos etc).

Testing: jdk/jdk/jfr

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.org/jdk/pull/26811/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26811&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8365636
  Stats: 88 lines in 33 files changed: 1 ins; 16 del; 71 mod
  Patch: https://git.openjdk.org/jdk/pull/26811.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26811/head:pull/26811

PR: https://git.openjdk.org/jdk/pull/26811