RFR 8138704: CertStatusReqItemV2 should not implement StatusRequest interface

[Jamil Nimeh]

Hello all,

While looking at CertStatusReqItemV2, I came across a left-over from 
early prototyping.  The class currently implements StatusRequest, but it 
really shouldn't.  It never caused a problem because StatusRequest 
requires the implementation of length and send methods, and that class 
needed those methods anyway.

So this webrev is for the removal of that implements directive and 
reduces the visibility of those two methods to package-private.

JBS: https://bugs.openjdk.java.net/browse/JDK-8138704
Webrev: http://cr.openjdk.java.net/~jnimeh/reviews/8138704/webrev.01/

Thanks,
--Jamil