RFR: JDK-8285307: remove unused os::available

[Matthias Baesken]

Seems int os::available(int fd, jlong *bytes) is not used any more and can be removed.

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Commit messages:
 - JDK-8285307

Changes: https://git.openjdk.java.net/jdk/pull/8327/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8327&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8285307
  Stats: 219 lines in 5 files changed: 0 ins; 219 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8327.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8327/head:pull/8327

PR: https://git.openjdk.java.net/jdk/pull/8327