RFR: JDK-8314197: AttachListener::pd_find_operation always returning nullptr

[Matthias Baesken]

AttachListener::pd_find_operation always returns nullptr and seems to be obsolete, so we could probably remove it and clean up the coding a bit.

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Commit messages:
 - JDK-8314197

Changes: https://git.openjdk.org/jdk/pull/15265/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15265&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8314197
  Stats: 24 lines in 6 files changed: 0 ins; 24 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/15265.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15265/head:pull/15265

PR: https://git.openjdk.org/jdk/pull/15265