RFR: 8311823: Remove JFR: Uninitialized EventEmitter::_thread_id field

[Elif Aslan]

[JDK-8311823](https://bugs.openjdk.org/browse/JDK-8311823)

Remove Uninitialized EventEmitter::_thread_id field from src/hotspot/share/jfr/leakprofiler/checkpoint/eventEmitter.hpp

GHA tests pass

Additional testing:
make test TEST=jdk/jfr

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Commit messages:
 - 8311823: Remove JFR: Uninitialized EventEmitter::_

Changes: https://git.openjdk.org/jdk/pull/15893/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15893&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8311823
  Stats: 1 line in 1 file changed: 0 ins; 1 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15893.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15893/head:pull/15893

PR: https://git.openjdk.org/jdk/pull/15893