RFR: 8300644: Remove gc/shenandoah/jni/TestStringCriticalWithDedup.java

[Erik Österlund]

The gc/shenandoah/jni/TestStringCriticalWithDedup.java test was designed to catch failure to pin strings being passed out to JNI critical users, because that used to be dangerous. After [JDK-8299673](https://bugs.openjdk.org/browse/JDK-8299673) that is not dangerous any longer. Conversely, now we kind of want deduplication to proceed regardless of JNI critical, which defeats the purpose of this test. It should be removed.

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Commit messages:
 - 8300644: Remove gc/shenandoah/jni/TestStringCriticalWithDedup.java

Changes: https://git.openjdk.org/jdk/pull/12089/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=12089&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8300644
  Stats: 167 lines in 1 file changed: 0 ins; 167 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12089.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12089/head:pull/12089

PR: https://git.openjdk.org/jdk/pull/12089