RFR: fix logic in PhaseIterGVN::add_users_to_worklist(), remove useless code from PhaseCCP::analyze()

[Roland Westrelin]

http://cr.openjdk.java.net/~roland/shenandoah/phaseX.cpp-fixes/webrev.00/

A small bug in PhaseIterGVN::add_users_to_worklist() and some useless
code now that we never add barriers on constant oops.

Roland.