RFR: 8330704: Clean up non-standard use of /** comments in some langtools tests

[Jonathan Gibbons]

Please review a simple change to clean up inappropriate use of `/**` comments in test code -- most notably to enclose the `jtreg` test description.

There is no change to the functionality of any test, and (obviously) all tests continue to pass.

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Commit messages:
 - JDK-8330704: Clean up non-standard use of /** comments in some langtools tests

Changes: https://git.openjdk.org/jdk/pull/18896/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18896&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8330704
  Stats: 44 lines in 22 files changed: 0 ins; 0 del; 44 mod
  Patch: https://git.openjdk.org/jdk/pull/18896.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18896/head:pull/18896

PR: https://git.openjdk.org/jdk/pull/18896