RFR: 8370071: Clarify jcmd Thread.print help message

[Sean Coffey]

Simple tweak to jcmd Thread.print help message

jdk_svc test group ran and green

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Commit messages:
 - 8370071

Changes: https://git.openjdk.org/jdk/pull/27861/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27861&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8370071
  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/27861.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27861/head:pull/27861

PR: https://git.openjdk.org/jdk/pull/27861