RFR: 8337982: Remove dead undef assrt0n

[Stefan Karlsson]

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.

Marked as reviewed by stefank (Reviewer).

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PR Review: https://git.openjdk.org/jdk/pull/20493#pullrequestreview-2225990729