RFR (S): 8232777: Rename G1Policy::_max_rs_length as it is no maximum

[Thomas Schatzl]

Hi all,

   can I have reviews for this small cleanup that renames 
G1Policy::_max_rs_length to just _rs_length because the contained value 
is simply no maximum. This causes some confusion down the line in its 
use (imo).

CR:
https://bugs.openjdk.java.net/browse/JDK-8232777
Webrev:
http://cr.openjdk.java.net/~tschatzl/8232777/webrev/
Testing:
local compilation

Thanks,
   Thomas