Disable heap iteration for Shenandoah in SA

[Aleksey Shipilev]

On 11/28/18 6:38 PM, Roman Kennke wrote:
> As Per pointed out in reviews, we cannot safely iterate objects in SA,
> because current implementation is size-based. This might just crash.
> Let's do the same as ZGC for now and disable it, and revert the other
> pieces.
> 
> http://cr.openjdk.java.net/~rkennke/disable-sa-heapdump/webrev.00/

Comment is incorrect, should be "Shenandoah":

 372        // Operation (currently) not supported with ZGC. Print

Then what Zhengyu said, we can remove cell_header_size completely?

-Aleksey