RFR (M): 8233588: Clean up SurvRateGroup

[Thomas Schatzl]

Hi all,

   can I have some reviews for this change that cleans up the 
SurvRateGroup class. In particular, while working with it I found that 
it contains two members that are duplicates of others.

This removed a few methods, which in turn made some others obsolete.

Further I tried to improve encapsulation so that not everyone needs to 
know all details down to SurvRateGroup.

That's why this change is a bit larger than you'd probably expect, but 
it contains a significant amount of code deletion! :)

CR:
https://bugs.openjdk.java.net/browse/JDK-8233588
Webrev:
http://cr.openjdk.java.net/~tschatzl/8233588/webrev/
Testing:
hs-tier1-5

Thanks,
   Thomas