RFR: 8333713: C2 SuperWord: cleanup in vectornode.cpp/hpp

[Emanuel Peter]

On Thu, 6 Jun 2024 13:52:56 GMT, Vladimir Kozlov <kvn at openjdk.org> wrote:

>> Removed dead code and renamed `superword` -> `auto_vectorization`, just like I had done in [JDK-8324750](https://bugs.openjdk.org/browse/JDK-8324750).
>
> Good.

Thanks @vnkozlov @chhagedorn for the reviews!

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PR Comment: https://git.openjdk.org/jdk/pull/19575#issuecomment-2154010958