RFR: 8370050: Shenandoah: Obsolete ShenandoahPacing option

[William Kemper]

ShenandoahPacing was removed in this release (26). Rather than have the JVM refuse to start if this option is given, it should give a warning that the option is removed and is ignored and will reject the option in JDK27.

Testing:

[0] % ./build/linux-x86_64-server-release/jdk/bin/java -XX:+UseShenandoahGC -XX:+UnlockExperimentalVMOptions -XX:+ShenandoahPacing --version
OpenJDK 64-Bit Server VM warning: Ignoring option ShenandoahPacing; support was removed in 26.0

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Commit messages:
 - Obsolete ShenandoahPacing option in 26 (pacing was removed in 26)

Changes: https://git.openjdk.org/jdk/pull/27859/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27859&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8370050
  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/27859.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27859/head:pull/27859

PR: https://git.openjdk.org/jdk/pull/27859