RFR: 8337982: Remove dead undef assrt0n

[duke]

On Wed, 7 Aug 2024 12:28:55 GMT, Casper Norrbin <duke at openjdk.org> wrote:

> Hello everyone,
> 
> `blockTree.cpp` contains an `#undef` that is never defined anywhere.
> This is dead code should be removed.
> 
> Thanks.

@caspernorrbin 
Your change (at version 1bc093001f75280acf13224d09959c06f3f5ae27) is now ready to be sponsored by a Committer.

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PR Comment: https://git.openjdk.org/jdk/pull/20493#issuecomment-2275209134