RFR: 8358598: PhaseIterGVN::PhaseIterGVN(PhaseGVN* gvn) doesn't use its parameter

[Francesco Andreuzzi]

As noted in the ticket, I propose a small cleanup of `PhaseIterGVN` since one of the constructors does not use its parameter.

-------------

Commit messages:
 - nn
 - cleanup

Changes: https://git.openjdk.org/jdk/pull/26617/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=26617&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8358598
  Stats: 17 lines in 4 files changed: 0 ins; 5 del; 12 mod
  Patch: https://git.openjdk.org/jdk/pull/26617.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/26617/head:pull/26617

PR: https://git.openjdk.org/jdk/pull/26617