RFR: 8336012: Fix usages of jtreg-reserved properties

[Christian Stein]

Please review this trivial test-only change to resolve a name clash with a jtreg-reserved property by removing the third option to control a test verbosity level via the `test.verbose` system property.

The fix assumes that the system property was only used in a manual scenario, like `make test TEST=...` and a `-Dtest.verbose=99` equivalent. For such scenarios, the other two names (for example `-DPrivateInvokeTest.verbose=99`) are still supported.

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Commit messages:
 - JDK-8336012: Fix usages of jtreg-reserved properties

Changes: https://git.openjdk.org/jdk/pull/20099/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=20099&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8336012
  Stats: 3 lines in 1 file changed: 0 ins; 2 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/20099.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20099/head:pull/20099

PR: https://git.openjdk.org/jdk/pull/20099