RFR: 8265435: Remove dummy lists in G1CalculatePointersClosure

[Albert Mingkun Yang]

Remove the dummy list and some general cleanup.

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Commit messages:
 - freelist

Changes: https://git.openjdk.java.net/jdk/pull/3568/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3568&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8265435
  Stats: 49 lines in 2 files changed: 15 ins; 31 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3568.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3568/head:pull/3568

PR: https://git.openjdk.java.net/jdk/pull/3568