RFR (S) 8242114: Shenandoah: remove ShenandoahHeapRegion::reset_alloc_metadata_to_shared

[Aleksey Shipilev]

RFE:
  https://bugs.openjdk.java.net/browse/JDK-8242114

This is a follow-up after removal of shared-alloc-counter (JDK-8241841) and removal of Traversal
(JDK- 8242082). ShenandoahHeapRegion::reset_alloc_metadata_to_shared is now the same as
ShenandoahHeapRegion::reset_alloc_metadata. Humongous allocation path also does not need resets,
because the alloc metadata is already clean there.

Webrev:
 https://cr.openjdk.java.net/~shade/8242114/webrev.01/

Testing: hotspot_gc_shenandoah

-- 
Thanks,
-Aleksey