RFR: 8270475: Remove unused G1STWDrainQueueClosure

[Thomas Schatzl]

Hi all,

  can I have reviews for this removal of unused code?

Testing: local compilation

Thanks,
  Thomas

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Commit messages:
 - Remove G1STWDrainQueueClosure

Changes: https://git.openjdk.java.net/jdk/pull/4782/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=4782&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8270475
  Stats: 23 lines in 1 file changed: 0 ins; 23 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4782.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4782/head:pull/4782

PR: https://git.openjdk.java.net/jdk/pull/4782