RFR: 8358633 : Test ThreadPoolExecutorTest::testTimedInvokeAnyNullTimeUnit is broken by JDK-8347491

[Viktor Klang]

It's too fragile to depend on generated NPE messages

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Commit messages:
 - Removing exception message check to avoid failures if helpful NPEs are turned off

Changes: https://git.openjdk.org/jdk/pull/25655/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25655&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8358633
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/25655.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25655/head:pull/25655

PR: https://git.openjdk.org/jdk/pull/25655