RFR: 8287227: Shenandoah: A couple of virtual thread tests failed with iu mode even without Loom enabled.

[Roland Westrelin]

With JDK-8277654, the load barrier slow path call doesn't produce raw
memory anymore but the IU barrier call still does. I propose removing
raw memory for that call too which also causes the assert that fails
to be removed.

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Commit messages:
 - fix

Changes: https://git.openjdk.java.net/jdk/pull/8958/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk&pr=8958&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8287227
  Stats: 290 lines in 2 files changed: 0 ins; 287 del; 3 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8958.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8958/head:pull/8958

PR: https://git.openjdk.java.net/jdk/pull/8958