RFR: 8138833: Remove CMMarkStack::drain

[Per Liden]

On 2015-10-03 21:01, Kim Barrett wrote:
> Please review this small change to remove some dead code from
> CMMarkStack.
>
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8138833
>
> Webrev:
> http://cr.openjdk.java.net/~kbarrett/8138833/webrev.00/

Looks good.

/Per