RFR: 8282348: Remove unused CardTable::dirty_card_iterate

[Albert Mingkun Yang]

Simple change of removing dead code.

Test: hotspot_gc

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Commit messages:
 - remove-dirty_card_iterate

Changes: https://git.openjdk.java.net/jdk/pull/7610/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=7610&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282348
  Stats: 30 lines in 2 files changed: 0 ins; 30 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/7610.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/7610/head:pull/7610

PR: https://git.openjdk.java.net/jdk/pull/7610