RFR: 8292607: Remove unused dirty and dirty_card_range_after_reset in CardTable

[Albert Mingkun Yang]

Trivial change of removing dead code.

Test: build

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Commit messages:
 - cardtable-remove-unused

Changes: https://git.openjdk.org/jdk/pull/9920/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=9920&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8292607
  Stats: 46 lines in 2 files changed: 0 ins; 46 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/9920.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/9920/head:pull/9920

PR: https://git.openjdk.org/jdk/pull/9920