RFR (S): 8184667: Clean up G1ConcurrentMark files

[Thomas Schatzl]

Hi all,

  can I have reviews for this code cleanup of G1ConcurrentMark* files?

The idea is to fix formatting, naming, assert strings, remove unused
variables and methods, some missing braces around statements, and look
into whether member visibility could be improved.

No actual behavior changes.

The CR contains references to a few other cleanup RFEs that I thought
would not fit perfectly.

CR:
https://bugs.openjdk.java.net/browse/JDK-8184667
Webrev:
http://cr.openjdk.java.net/~tschatzl/8184667/webrev/
Testing:
jprt

Thanks,
  Thomas