RFR (S): 8201640: Use _ref_processor_* member variables directly in G1CollectedHeap

[Thomas Schatzl]

Hi all,

  can I have reviews for this minor cleanup that removes the use of
getters to the various ref_processor members in G1CollectedHeap by
direct access?

CR:
https://bugs.openjdk.java.net/browse/JDK-8201640
Webrev:
http://cr.openjdk.java.net/~tschatzl/8201640/
Testing:
hs-tier1-3 with other changes, local compilation

Thanks,
  Thomas