RFR (S): 8178151: Clean up G1RemSet files

[Thomas Schatzl]

Hi all,

  can I have reviews for this small change that is supposed to tighten
the interface and clean up documentation for the g1Remset* files
including some better naming?

[Note: I already sent this out for review two months ago in that big
RFR thread with 7 changes. However, so much time has been elapsed since
then, and everything based on this has been pushed, so I figured it
would be simpler to just make an extra RFR request]

CR:
https://bugs.openjdk.java.net/browse/JDK-8178151
Webrev:
http://cr.openjdk.java.net/~tschatzl/8178151/webrev.1/
Testing:
jprt

Thanks,
  Thomas