RR: 8201244: Clean out unnecessary includes of heap headers

[Stefan Karlsson]

Hi all,

Please review this patch to remove some unnecessary includes of the 
different GC heap headers.

http://cr.openjdk.java.net/~stefank/8201244/webrev.01
https://bugs.openjdk.java.net/browse/JDK-8201244

thanks,
StefanK