RFR: 8266491: Remove resolve and obj_equals leftovers from BarrierSetAssembler

[Roman Kennke]

Shenandoah used to require resolve() and obj_equals() in its first incarnation in JDK12. This is long obsolete, and the corresponding code can be removed from BarrierSetAssembler. It also makes the code less confusing because obj_equals() and resolve() have both been rather clunky and given that they now do nothing (and there are other resolve* methods in BSA too), it's not even clear what they would be supposed to do. It also makes life easier for porters to other platforms.

Testing:
 - [x] Build x86_64, x86_32
 - [x] hotspot_gc_shenandoah
 - [ ] tier1, tier2
 - [ ] Build arm, aarch64 (by GH-actions)

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Commit messages:
 - 8266491: Remove resolve and obj_equals leftovers from BarrierSetAssembler

Changes: https://git.openjdk.java.net/jdk/pull/3850/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3850&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266491
  Stats: 168 lines in 25 files changed: 0 ins; 161 del; 7 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3850.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3850/head:pull/3850

PR: https://git.openjdk.java.net/jdk/pull/3850