RFR: Cleanup obsolete Shenandoah changes in ciInstanceKlass

[Aleksey Shipilev]

On 11/19/18 10:45 AM, Roman Kennke wrote:
> I believe the changes in ciInstanceKlass::get_canonical_holder() are a
> leftover from *long* time ago when we did not create extra slices for -8
> offset. We can remove it.
> 
> Testing: tier3_gc_shenandoah
> 
> http://cr.openjdk.java.net/~rkennke/cleanup-ciinstanceklass/webrev.00/

Looks good to me.

-Aleksey