RFR: JDK-8285439: remove unused os::fsync

[Matthias Baesken]

Please review this small change; it removes the unused os::fsync function .
Thanks, Matthias

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Commit messages:
 - JDK-8285439

Changes: https://git.openjdk.java.net/jdk/pull/8358/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8358&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285439
  Stats: 20 lines in 3 files changed: 0 ins; 20 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8358.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8358/head:pull/8358

PR: https://git.openjdk.java.net/jdk/pull/8358