RFR: 8253226: Shenandoah: remove unimplemented ShenandoahStrDedupQueue::verify

[Aleksey Shipilev]

`ShenandoahStrDedupQueue` defers to super-class that in turn calls `verify_impl()`. `verify()` is left unused and
unimplemented. Static analysis complains about it.

Testing: Linux x86_64 fastdebug tier1_gc_shenandoah

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Commit messages:
 - 8253226: Shenandoah: remove unimplemented ShenandoahStrDedupQueue::verify

Changes: https://git.openjdk.java.net/jdk/pull/203/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=203&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8253226
  Stats: 2 lines in 1 file changed: 0 ins; 2 del; 0 mod
  Patch: https://git.openjdk.java.net/jdk/pull/203.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/203/head:pull/203

PR: https://git.openjdk.java.net/jdk/pull/203