RFR: Rename "cancel_concgc" to "cancel_gc"

[Roman Kennke]

Am 15.05.2018 um 18:46 schrieb Aleksey Shipilev:
> http://cr.openjdk.java.net/~shade/shenandoah/rename-cancel/webrev.01/
> 
> It always irks me to see "Cancel concurrent GC" from Degenerated -> Full GC upgrade.
> 
> Testing: hotspot_gc_shenandoah, eyeballing -Xlog:gc
> 
> Thanks,
> -Aleksey
> 

This makes sense. Go!

Roman