RFR: 8348575: Remove unused typedef SpinLockT

[Hamlin Li]

Hi,
Can you help to review this simple patch?

SpinLockT is typedef'ed, but there is no usage of it. I think this is a legacy code from long time before. Also remove/modify some related comment.

Thanks

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Commit messages:
 - Initial commit

Changes: https://git.openjdk.org/jdk/pull/23298/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=23298&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8348575
  Stats: 11 lines in 1 file changed: 0 ins; 9 del; 2 mod
  Patch: https://git.openjdk.org/jdk/pull/23298.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/23298/head:pull/23298

PR: https://git.openjdk.org/jdk/pull/23298