RFR: 8330419: Unused code in ConnectionGraph::specialize_castpp

[Fei Yang]

Please review this small code cleanup change.

Noticed that `minus_one` local created in `ConnectionGraph::specialize_castpp` which is added by JDK-8316991 is never used.
I think it should be safe to remove this. Also renamed `boll` to `bol` to be consistent in naming with other places where we create a `BoolNode`.

Tersting: tier1 tested on linux-aarch64 (release & fastdebug)

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Commit messages:
 - cleanup

Changes: https://git.openjdk.org/jdk/pull/18805/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=18805&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8330419
  Stats: 5 lines in 1 file changed: 0 ins; 1 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/18805.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18805/head:pull/18805

PR: https://git.openjdk.org/jdk/pull/18805