RFR: More cleanup

[Roman Kennke]

This removes some more unnecessary diffs between jdk9 baseline and
shenandoah:

http://cr.openjdk.java.net/~rkennke/cleanup/webrev.00/

There's not much of significance here, except that it brings our repo
closer to our baseline.

The two most interesting ones:
- In ThreadLocalAllocBuffer, we added 1 extra word for the brooks ptr
to the end reserve. I believe this has been added a long time ago, and
probably for the bug we resolved yesterday :-) In any case, it's not
needed.
- In JVM_Clone, we're doing a read-barrier when sticking an oop into a
Handle. However, there's no guarantee that when we're crossing a
safepoint there, that the oop is still valid for reading. Barriers
should therefore always be done after pulling the oop out of the
Handle. Done with this patch.

Ok?

Roman