RFR (S): 8234587: Rename the SurvRateGroup class to G1SurvRateGroup

[Thomas Schatzl]

Hi all,

   can I have reviews for this addition of a "G1" prefix for the name of 
the SurvRateGroup class after moving it into correctly named files jusst 
earlier?

Based on JDK-8234587.

CR:
https://bugs.openjdk.java.net/browse/JDK-8234587
Webrev:
http://cr.openjdk.java.net/~tschatzl/8234587/webrev/
Testing:
local compilation

Thanks,
   Thomas