RFR: 8307571: Remove unused SomeConstants in WatcherThread class

[Zhengyu Gu]

A trivial cleanup

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Commit messages:
 - 8307571: Remove unused SomeConstants in WatcherThread class

Changes: https://git.openjdk.org/jdk/pull/13856/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=13856&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8307571
  Stats: 5 lines in 1 file changed: 0 ins; 5 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/13856.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13856/head:pull/13856

PR: https://git.openjdk.org/jdk/pull/13856