RFR: 8133825: Remove the class G1CollectorPolicyExt

[Erik Helin]

Hi all,

after the patch "8133821: Refactor initialization of the heap and the
collector policy", the class G1CollectorPolicyExt can be removed.

Webrev:
http://cr.openjdk.java.net/~ehelin/8133825/webrev.00/

Bug:
https://bugs.openjdk.java.net/browse/JDK-8133825

Testing:
JPRT

Thanks,
Erik