RFR: 8344339: GenShen: Avoid using namespaces

[William Kemper]

Namespaces are contrary to hotspot style guide: https://github.com/openjdk/jdk/blob/master/doc/hotspot-style.md#namespaces

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Commit messages:
 - Avoid using namespaces

Changes: https://git.openjdk.org/shenandoah/pull/542/files
  Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=542&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8344339
  Stats: 4 lines in 1 file changed: 0 ins; 1 del; 3 mod
  Patch: https://git.openjdk.org/shenandoah/pull/542.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/542/head:pull/542

PR: https://git.openjdk.org/shenandoah/pull/542