RFR: 8253516: ZGC: Remove card table functions

[Thomas Schatzl]

On Wed, 23 Sep 2020 07:50:45 GMT, Stefan Karlsson <stefank at openjdk.org> wrote:

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

Lgtm and trivial

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Marked as reviewed by tschatzl (Reviewer).

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