RFR: 8198432: Remove Thread extension point

[David Holmes]

Hi Stefan,

On 26/02/2018 8:54 PM, Stefan Johansson wrote:
> Hi,
> 
> Please review this small change to remove a now unused extension point.

Unused by Oracle. While I'm glad to see this gone we need to wait and 
see if anyone else had utilized these "extension" points.

Thanks,
David

> Links
> JBS: https://bugs.openjdk.java.net/browse/JDK-8198432
> Webrev: http://cr.openjdk.java.net/~sjohanss/8198432/00/
> 
> Summary
> The Thread class extension support made it possible to add extra data to 
> it. This is no longer needed since the internal code using it has been 
> removed.
> 
> Testing
> Built locally and through Mach5.
> 
> Thanks,
> Stefan