[jdk11u-dev] RFR: 8230841: Remove oopDesc::equals()

[Aleksey Shipilev]

This is the second patch in the series to cleanup/revert the GC BarrierSets to most current state. See the dependent ("this issue blocks" links) issues to see what is next.

The equals APIs were added for Shenandoah GC, in the incarnation that exposed both from- and to-copies to the runtime system (see JDK-8199781). Since then, Shenandoah greatly simplified this by switching to a strong to-space invariant, which obviates the need for this API. Therefore, it was removed in JDK 14. This patch reverts JDK 11 parts to that shape as well, which should simplify 11u maintenance.

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Commit messages:
 - Backport 2d6874b861270ea67322d5976a30202bdb6adb1c

Changes: https://git.openjdk.java.net/jdk11u-dev/pull/204/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk11u-dev&pr=204&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8230841
  Stats: 84 lines in 33 files changed: 0 ins; 11 del; 73 mod
  Patch: https://git.openjdk.java.net/jdk11u-dev/pull/204.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk11u-dev pull/204/head:pull/204

PR: https://git.openjdk.java.net/jdk11u-dev/pull/204