RFR: 8253516: ZGC: Remove card table functions

[Stefan Karlsson]

A few functions were not removed from ZCollectedHeap when the card table functions were moved out of CollectedHeap
(JDK-8195103). Remove them.

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Commit messages:
 - 8253516: ZGC: Remove card table functions

Changes: https://git.openjdk.java.net/jdk/pull/316/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=316&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253516
  Stats: 20 lines in 2 files changed: 0 ins; 20 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/316.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/316/head:pull/316

PR: https://git.openjdk.java.net/jdk/pull/316