RFR: Cleanup C2 parse sources

[Roman Kennke]

This cleans up some more leftover stuff in C2, this time in parse*
source files.

The arrayaddressing() changes is leftovers from when we inserted
explicit barriers and not needed anymore.

The block in parse3.cpp used to mark String backing arrays as stable,
but we disable this optimization by default anyway, and JMM-wise we
consider it questionable, so it doesn't seem important enough to upstream.

Testing: tier3_gc_shenandoah

http://cr.openjdk.java.net/~rkennke/c2-cleanup-parse/webrev.00/

Ok?

Roman