RFR: 8332095: GenShen: Move more generational mode members out of shHeap [v2]

[William Kemper]

> The following members and methods in shHeap are only used in generational mode and can be moved out of common code:
> * ShenandoahHeap::cancel_old_gc
> * ShenandoahHeap::transfer_old_pointers_from_satb
> * ShenandoahHeap::_is_aging_cycle

William Kemper has updated the pull request incrementally with one additional commit since the last revision:

  Update confusing comment

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Changes:
  - all: https://git.openjdk.org/shenandoah/pull/431/files
  - new: https://git.openjdk.org/shenandoah/pull/431/files/b875957d..75fdfdbc

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=shenandoah&pr=431&range=01
 - incr: https://webrevs.openjdk.org/?repo=shenandoah&pr=431&range=00-01

  Stats: 2 lines in 1 file changed: 1 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/shenandoah/pull/431.diff
  Fetch: git fetch https://git.openjdk.org/shenandoah.git pull/431/head:pull/431

PR: https://git.openjdk.org/shenandoah/pull/431