8155099: Remove duplicate comments from G1Policy

[Erik Helin]

Hi all,

this patch removes some duplicated comments originating from the patch
"Turn G1Policy into an interface". The comments belong in the interface,
not in the implementation.

Bug:
https://bugs.openjdk.java.net/browse/JDK-8155099

Webrev:
http://cr.openjdk.java.net/~ehelin/8155099/webrev.00/

Testing:
- Only comments have been removed

Thanks,
Erik