RFR: 8286480: Remove the c1 getEventWriter() intrinsic to simplify post-Loom integration platform-porting efforts

[Markus Grönlund]

Greetings,

The C1 intrinsic for getEventWriter() did not materialize and is currently only bouncing a platform-specific stub to enter the VM, putting an unnecessary burden on post-Loom integration platform-porting efforts.

The platform-specific stub for C2, jfr_write_checkpoint, is still needed but is only called if a java/lang/VirtualThread is mounted. As such, it could be left unimplemented.

Testing: jdk_jfr

Thanks
Markus

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Commit messages:
 - 8286480

Changes: https://git.openjdk.java.net/jdk/pull/8631/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8631&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8286480
  Stats: 83 lines in 9 files changed: 5 ins; 68 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8631.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8631/head:pull/8631

PR: https://git.openjdk.java.net/jdk/pull/8631