RFR: CODETOOLS-7903096: remove old @author tags

[Jonathan Gibbons]

Please review a patch to remove the few remaining `@author` tags, and to update the CONTRIBUTORS file accordingly.
The authors in the legacy tags are now in the CONTRIBUTORS file, which is also updated to describe the use of SCM metadata for contributors and contributions, which is a much better mechanism than poorly maintained `@author` tags.

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Commit messages:
 - CODETOOLS-7903096: remove old @author tags

Changes: https://git.openjdk.java.net/jtreg/pull/56/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jtreg&pr=56&range=00
  Issue: https://bugs.openjdk.java.net/browse/CODETOOLS-7903096
  Stats: 40 lines in 21 files changed: 5 ins; 29 del; 6 mod
  Patch: https://git.openjdk.java.net/jtreg/pull/56.diff
  Fetch: git fetch https://git.openjdk.java.net/jtreg pull/56/head:pull/56

PR: https://git.openjdk.java.net/jtreg/pull/56