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

[Daniel Jeliński]

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.

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Commit messages:
 - Update copyright
 - Remove outdated comment
 - Remove nop list

Changes: https://git.openjdk.org/jdk/pull/27117/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=27117&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8366971
  Stats: 83 lines in 11 files changed: 1 ins; 77 del; 5 mod
  Patch: https://git.openjdk.org/jdk/pull/27117.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/27117/head:pull/27117

PR: https://git.openjdk.org/jdk/pull/27117