RFR: Remove narrowOop variants of oopDesc::equals and related methods

[Roman Kennke]

Turns out that we don't actually need the narrowOop versions of
oopDesc::equals() and all the related methods. This patch removes them.
The remaining stuff is being worked on upstream right now, and will
hopefully go away soon too.

http://cr.openjdk.java.net/~rkennke/equals-narrowop/webrev.00/

Test: hotspot_gc_shenandoah fastdebug

Ok?

Roman