RFR: Remove ConstantOopWriteValue::write_on in favor of upstream fix

[Roman Kennke]

Am 14.03.2018 um 18:11 schrieb Aleksey Shipilev:
> http://cr.openjdk.java.net/~shade/shenandoah/revert-cowv-workaround/webrev.01/
> 
> This reverts our workaround in ConstantOopWriteValue [1], because now the proper upstream fix
> arrived, that enters the VM state properly. This also removes the #include added by Zhengyu for
> non-PCH build, because we do not have changes in debugInfo.* anymore.
> 
> Testing: hotspot_gc_shenandoah
> 
> Thanks,
> -Aleksey
> 
> [1] http://hg.openjdk.java.net/shenandoah/jdk10/rev/4d0b215d0eca
> 

Good! Go!