RFR (S): 8202780: Remove EnqueueTask related code from ReferenceProcessor after JDK-8202017

[Kim Barrett]

> On May 8, 2018, at 9:17 AM, Thomas Schatzl <thomas.schatzl at oracle.com> wrote:
> 
> Hi all,
> 
>  in JDK-8202017 we removed the separate enqueue references phase for
> all collectors; can I have reviews to remove some support code that is
> now dead code?
> 
> CR:
> https://bugs.openjdk.java.net/browse/JDK-8202780
> Webrev:
> http://cr.openjdk.java.net/~tschatzl/8202780/webrev/
> Testing:
> local compilation
> 
> Thanks,
>  Thomas

Looks good.