RFR (XS) 8212025: Remove collector_present variable from ThreadHeapSampler

[Per Liden]

Looks good.

/Per

On 10/10/2018 10:15 PM, JC Beyler wrote:
> Hi all,
> 
> Here is a tiny webrev to remove the _collectors_present member that is 
> now unused. I forgot to remove it when I did the fix for JDK-8211950.
> 
> Webrev: http://cr.openjdk.java.net/~jcbeyler/8212025/webrev.00/ 
> <http://cr.openjdk.java.net/%7Ejcbeyler/8212025/webrev.00/>
> Bug: https://bugs.openjdk.java.net/browse/JDK-8212025
> 
> My apologies,
> Jc