RFR: 8272114: Unused _last_state in osThread_windows

[Yi Yang]

Unused _last_state in osThread_windows， its getter and setter can be removed as well.

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Commit messages:
 - remove

Changes: https://git.openjdk.java.net/jdk/pull/5572/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=5572&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8272114
  Stats: 7 lines in 1 file changed: 0 ins; 7 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/5572.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/5572/head:pull/5572

PR: https://git.openjdk.java.net/jdk/pull/5572