RFR (XS): JDK-8204084: Remove the G1RSBarrierRegionFilter develop flag

[Thomas Schatzl]

Hi all,

  can I have reviews for this small change that removes the
G1RSBarrierRegionFilter develop flag from G1 code that is implemented
in a very incomplete way, and since I do not see a point fixing that I
suggest removing it.

CR:
https://bugs.openjdk.java.net/browse/JDK-8204084
Webrev:
http://cr.openjdk.java.net/~tschatzl/8204084/webrev/
Testing:
compilation

Thanks,
  Thomas