RFR: 8249528: Remove obsolete comment in G1RootProcessor::process_java_roots

Tue Apr 6 08:00:55 UTC 2021

Updating the obsolete comment and some trivial change of removing dead code in related files.

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Commit messages:
 - root

Changes: https://git.openjdk.java.net/jdk/pull/3352/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3352&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8249528
  Stats: 42 lines in 5 files changed: 19 ins; 13 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3352.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3352/head:pull/3352

PR: https://git.openjdk.java.net/jdk/pull/3352