RFR: 8282728: Remove unused BlockOffsetArray::Action

[Albert Mingkun Yang]

Simple change of removing dead code.

Test: hotspot_gc

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Commit messages:
 - bot-action

Changes: https://git.openjdk.java.net/jdk/pull/7726/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7726&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282728
  Stats: 42 lines in 2 files changed: 0 ins; 32 del; 10 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7726.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7726/head:pull/7726

PR: https://git.openjdk.java.net/jdk/pull/7726