RFR: 8281035: Serial: Move RemoveForwardedPointerClosure to local scope

[Albert Mingkun Yang]

Simple change of moving `RemoveForwardedPointerClosure` from shared code to Serial code.

Test: hotspot_gc

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Commit messages:
 - serial-promotion-failure

Changes: https://git.openjdk.java.net/jdk/pull/7301/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7301&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8281035
  Stats: 27 lines in 3 files changed: 13 ins; 11 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7301.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7301/head:pull/7301

PR: https://git.openjdk.java.net/jdk/pull/7301