RFR: 8315875: GenShen: Remove heap mode check from ShenandoahInitLogger

[William Kemper]

There are some additional improvements to the init logger that should be easy to upstream.

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Commit messages:
 - Merge branch 'shenandoah-master' into isolate-shenandoah-heap
 - Prototype isolation of shenandoah heap with gc init logger

Changes: https://git.openjdk.org/shenandoah/pull/320/files
 Webrev: https://webrevs.openjdk.org/?repo=shenandoah&pr=320&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315875
  Stats: 179 lines in 7 files changed: 130 ins; 39 del; 10 mod
  Patch: https://git.openjdk.org/shenandoah/pull/320.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/320/head:pull/320

PR: https://git.openjdk.org/shenandoah/pull/320