[15] RFR 8242375: Shenandoah: Remove ShenandoahHeuristic::record_gc_start/end methods

[Zhengyu Gu]

Please review this patch to remove 
ShenandoahHeuristic::record_gc_start()/end() methods, they have no 
implementation and are called from wrong places.

Bug: https://bugs.openjdk.java.net/browse/JDK-8242375
Webrev: http://cr.openjdk.java.net/~zgu/JDK-8242375/webrev.00/index.html


Test:
   hotspot_gc_shenandoah


Thanks,

-Zhengyu