RFR: 8265012: Shenandoah: Backout JDK-8264718

[Zhengyu Gu]

It turns out that enquening string deduplication candidates during concurrent root scanning may result lock rank inversion between stack watermark lock and string dedup queue lock, if the scanning is triggered by stack watermark and dedup buffer happens to be full.

Backout JDK-8264718 for now, will retry after Kim's string deduplication refactoring.

Test:
- [x] hotspot_gc_shenandoah

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Commit messages:
 - JDK-8265012

Changes: https://git.openjdk.java.net/jdk/pull/3423/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=3423&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8265012
  Stats: 69 lines in 5 files changed: 26 ins; 39 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk/pull/3423.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/3423/head:pull/3423

PR: https://git.openjdk.java.net/jdk/pull/3423