RFR: 8134509: G1ParCopyClosure does not need a ReferenceProcessor

[Erik Helin]

Hi all,

this small patch removes an unused argument to the constructor of
G1ParCopyClosure. The argument ReferenceProcessor* rp is never used and
can therefore be removed, the getter method rp() can therefore also be
removed.

Webrev:
http://cr.openjdk.java.net/~ehelin/8134509/webrev.00/

Bug:
https://bugs.openjdk.java.net/browse/JDK-8134509

Testing:
JPRT

Thanks,
Erik