RFR: Remove safe_equals()

[Roman Kennke]

A looong while ago we introduced oopDesc::safe_equals() as a way to do
efficient object comparison without GC barriers, but also verify that
we're actually comparing to-space copies. It turned out that the only
place where we ever needed it was in ReferenceProcessor, and even there
it never triggered. Usage there can be reasoned about well enough, I
propose to drop safe_equals() and related code to further our reduce
upstream diff.

http://cr.openjdk.java.net/~rkennke/remove-safeeq/webrev.00/

For god-knows-what-reason, there's a missing BarrierSet fwd decl in
templateTable.hpp that has previously been 'covered' by our added
barrierSet.hpp inclusion in oop.hpp. No idea why upstream hasn't been
hit by this.?

Ok to push?

Roman