RFR: 7903055: Replace `junit.jar` with `junit-platform-console-standalone` artifact

[Christian Stein]

https://bugs.openjdk.java.net/browse/CODETOOLS-7903055

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Commit messages:
 - Restore updated comment
 - Replace `junit.jar` with `junit-platform-console-standalone` artifact

Changes: https://git.openjdk.java.net/jtreg/pull/63/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jtreg&pr=63&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903055
  Stats: 56 lines in 3 files changed: 1 ins; 47 del; 8 mod
  Patch: https://git.openjdk.java.net/jtreg/pull/63.diff
  Fetch: git fetch https://git.openjdk.java.net/jtreg pull/63/head:pull/63

PR: https://git.openjdk.java.net/jtreg/pull/63