RFR: 8280419: Remove dead code related to VerifyThread and verify_thread()

[David Holmes]

On Fri, 10 Feb 2023 02:12:59 GMT, David Holmes <dholmes at openjdk.org> wrote:

> This is code that was copied from the sparc port into the arm, ppc and s390 ports, but was never actually implemented.
> 
> I can't really test those platforms, but hopefully GHA builds will suffice, otherwise I need the various porters to confirm the changes.
> 
> Thanks.

All cross-compilation builds successful.

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PR: https://git.openjdk.org/jdk/pull/12506