RFR: Trivial dead code cleanup

[Zhengyu Gu]

A trivial cleanup of dead code.

Webrev: 
http://cr.openjdk.java.net/~zgu/shenandoah/deadcode-cleanup/webrev.00/index.html


Test:

   hotspot_gc_shenandoah on Linux 64 (fastdebug + release)

Thanks,

-Zhengyu