RFR (XS): 8224038: Fix remaining InCSetState mentions

[Thomas Schatzl]

Hi all,

  in JDK-8200545 there has been some renaming of the InCSetState class
to G1RegionAttr class.

Some comments and class names still mention it.

This change fixes this.

CR:
https://bugs.openjdk.java.net/browse/JDK-8224038
Webrev:
http://cr.openjdk.java.net/~tschatzl/8224038/webrev/
Testing:
local compilation

Thanks,
  Thomas