RFR: Minor cleanup of Shenandoah SA

[Roman Kennke]

Good! Thank you!

Roman


> - Delete an obsoleted/commented out line.
> - Rename SHENANDOAH_HEAP to SHENANDOAH to be consistent with other GCs.
> 
> Webrev: http://cr.openjdk.java.net/~zgu/shenandoah/minor_sa_fix/webrev.00/
> 
> Test:
> 
>   hotspot_serviceability, gc_shenandoah_tier1
> 
> Thanks,
> 
> -Zhengyu