RFR: 8316148: Remove sun/tools/jhsdb/JStackStressTest.java from problem list

[Chris Plummer]

[JDK-8276210](https://bugs.openjdk.org/browse/JDK-8276210) no longer seems to be reproducing, even before [JDK-8313800](https://bugs.openjdk.org/browse/JDK-8313800) was just pushed. I'm not sure what may have fixed it, but even if the bug was potentially still there, it has likely been fixed by [JDK-8313800](https://bugs.openjdk.org/browse/JDK-8313800). `sun/tools/jhsdb/JStackStressTest.java` should be removed from the problem list.

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Commit messages:
 - remove from problem list

Changes: https://git.openjdk.org/jdk/pull/15697/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15697&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8316148
  Stats: 2 lines in 1 file changed: 0 ins; 2 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15697.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15697/head:pull/15697

PR: https://git.openjdk.org/jdk/pull/15697