RFR: 8151539: Remove duplicate AlwaysTrueClosures

[Stefan Karlsson]

Hi all,

Please review this patch to remove a bunch of redundant 
AlwaysTrueClosure classes.

http://cr.openjdk.java.net/~stefank/8151539/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8151539

I've created an overloaded JNIHandles::weak_oops_do that uses its own 
AlwaysTrueClosure classes. This way callers of JNIHandles::weak_oops_do, 
that don't want to filter out any oops, can call the overloaded version 
without providing an instance of BoolObjectClosure.

Thanks,
StefanK