RFR: 8291021: JFR: Only one finished state in ChunkHeader class

[Erik Gahlin]

Could I have a review of PR that removes the field isFinished in the ChunkHeader class. It's sufficient with the finished field. 

Testing: jdk/jdk/jfr

Thanks
Erik

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Commit messages:
 - Initial

Changes: https://git.openjdk.org/jdk/pull/9639/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9639&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8291021
  Stats: 4 lines in 1 file changed: 0 ins; 2 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/9639.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9639/head:pull/9639

PR: https://git.openjdk.org/jdk/pull/9639