RFR: 8197845: Remove unnecessary method G1CollectedHeap::create_g1_policy

[Erik Helin]

Hi all,

this patch removes the no longer needed method 
G1CollectedHeap::create_g1_policy. Since that method is the sole content 
of the file g1CollectedHeap_ext.cpp, that file is also removed as part 
of this patch.

Issue:
https://bugs.openjdk.java.net/browse/JDK-8197845

Patch:
http://cr.openjdk.java.net/~ehelin/8197845/00/

Testing:
- make run-test-tier1 on Linux x86-64

Thanks,
Erik