RFR: 8366971: C2: Remove unused nop_list from PhaseOutput::init_buffer

[Dean Long]

On Fri, 5 Sep 2025 13:02:00 GMT, Daniel Jeliński <djelinski at openjdk.org> wrote:

> The nop list has never been used in the history of OpenJDK. Let's clean it up.
> 
> Tested with Mach5 tier 1-5, no related failures.

Looks good.

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Marked as reviewed by dlong (Reviewer).

PR Review: https://git.openjdk.org/jdk/pull/27117#pullrequestreview-3198456672