RFR (XS): 8054341: Remove some obsolete code in G1CollectedHeap class

[Thomas Schatzl]

Hi all,

  can I have reviews for this small change that removes some dead code
in the G1CollectedHeap files?

CR:
https://bugs.openjdk.java.net/browse/JDK-8054341
Webrev:
http://cr.openjdk.java.net/~tschatzl/8054341/webrev/
Testing:
jprt

Thanks,
  Thomas