[11u] RFR (S) 8245026: PsAdaptiveSizePolicy::_old_gen_policy_is_ready is unused

[Aleksey Shipilev]

Original RFE:
   https://bugs.openjdk.java.net/browse/JDK-8245026
   https://github.com/openjdk/jdk/commit/a8e3eabb

I would like to backport this for 11.0.11 parity. The patch does not apply cleanly to 11u, because 
the code is slightly different, notably in constructor initialization.

11u webrev:
   https://cr.openjdk.java.net/~shade/8245026/webrev.11u.01/

Testing: tier{1,2}

-- 
Thanks,
-Aleksey