RFR: 8264548: Dependencies: ClassHierarchyWalker::is_witness() cleanups [v2]

[Vladimir Ivanov]

> Simplify `ClassHierarchyWalker::is_witness()`.
> 
> Testing: hs-tier1 - hs-tier4.

Vladimir Ivanov has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains one additional commit since the last revision:

  Refactor ClassHierarchyWalker::is_witness()

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/3297/files
  - new: https://git.openjdk.java.net/jdk/pull/3297/files/fc92da2e..b7f31326

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3297&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3297&range=00-01

  Stats: 3498 lines in 125 files changed: 2719 ins; 306 del; 473 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3297.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3297/head:pull/3297

PR: https://git.openjdk.java.net/jdk/pull/3297