RFR (XXS): 8232260: Remove g1 prefix in G1CollectedHeap::g1_hot_card_cache() getter

[Thomas Schatzl]

Hi,

   can I have reviews for this small cleanup that removes some "g1_" 
prefix from some getter and some related unnecessary friend declaration.


CR:
https://bugs.openjdk.java.net/browse/JDK-8232260
Webrev:
http://cr.openjdk.java.net/~tschatzl/8232260/webrev/
Testing:
local compilation

Thanks,
   Thomas