RFR: 8253586: C2: Clean up unused PhaseIterGVN::init_worklist()

[Roberto Castaneda Lozano]

Remove unused method `PhaseIterGVN::init_worklist(Node *)`.

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

Commit messages:
 - 8253586: C2: Clean up unused PhaseIterGVN::init_worklist()

Changes: https://git.openjdk.java.net/jdk/pull/334/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=334&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253586
  Stats: 26 lines in 2 files changed: 0 ins; 26 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/334.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/334/head:pull/334

PR: https://git.openjdk.java.net/jdk/pull/334