RFR: 8371922: Remove unused NonblockingQueue class

[Kim Barrett]

Please review this trivial change that removes the unused NonblockingQueue
utility class and its associated gtests.

Testing: mach5 tier1

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Commit messages:
 - remove NonblockingQueue

Changes: https://git.openjdk.org/jdk/pull/28330/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=28330&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8371922
  Stats: 667 lines in 3 files changed: 0 ins; 667 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/28330.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/28330/head:pull/28330

PR: https://git.openjdk.org/jdk/pull/28330