RFR: 8342119: Shenandoah: Remove extra ShenandoahUpdateRefsClosure [v2]

[Aleksey Shipilev]

> We have a duplicate `ShenandoahUpdateRefsClosure`, which we use in a few places. For bulk GC operations, we have `ShenandoahConcUpdateRefsClosure` and `ShenandoahSTWUpdateRefsClosure` that are semantically similar to that one. We can drop the `ShenandoahUpdateRefsClosure` in favor of these two existing ones. 
> 
> Additional testing:
>  - [x] Linux x86_64 server fastdebug, `hotspot_gc_shenandoah`
>  - [x] Performance tests (no regressions)

Aleksey Shipilev has updated the pull request with a new target base due to a merge or a rebase. The incremental webrev excludes the unrelated changes brought in by the merge/rebase. The pull request contains three additional commits since the last revision:

 - Merge branch 'master' into JDK-8342119-shenandoah-remove-extra-ur-cl
 - Switch back to non-concurrent closure, rename update methods
 - Fix

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/21517/files
  - new: https://git.openjdk.org/jdk/pull/21517/files/f930e5a4..8e0727da

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=21517&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=21517&range=00-01

  Stats: 18413 lines in 583 files changed: 14207 ins; 1972 del; 2234 mod
  Patch: https://git.openjdk.org/jdk/pull/21517.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/21517/head:pull/21517

PR: https://git.openjdk.org/jdk/pull/21517