RFR: 8280419: Remove dead code related to VerifyThread and verify_thread() [v3]

[David Holmes]

> 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.

David Holmes has updated the pull request incrementally with two additional commits since the last revision:

 - Merge branch '8280419-verifyThread' of github.com:dholmes-ora/jdk into 8280419-verifyThread
 - Fix copyright.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12506/files
  - new: https://git.openjdk.org/jdk/pull/12506/files/96f6b52e..3d3031ad

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12506&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12506&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jdk/pull/12506.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12506/head:pull/12506

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